Linux server .so files not loaded

Our mobile project has a multiplayer server which will run on linux. We build the server with Target Platform set to linux and Server Build ticked on the Build Settings window in Unity Editor on Windows.

The server hangs / soft crashes, since the libs cannot be loaded:

 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0.so
 Fallback handler could not load library /local/game/server_Data/Mono/FirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0.so
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0.so
 Fallback handler could not load library /local/game/server_Data/Mono/FirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0.so
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0.so
 Fallback handler could not load library /local/game/server_Data/Mono/FirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0.so
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0.so
 Fallback handler could not load library /local/game/server_Data/Mono/FirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0.so
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0.so
 Fallback handler could not load library /local/game/server_Data/Mono/FirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0.so
 Fallback handler could not load library /local/game/server_Data/Mono/libFirebaseCppApp-8_9_0
 Could not resolve all Firebase dependencies System.TypeInitializationException: The type initializer for 'Firebase.FirebaseApp' threw an exception. ---> System.TypeInitializationException: The type initializer for 'Firebase.LogUtil' threw an exception. ---> System.TypeInitializationException: The type initializer for 'Firebase.AppUtilPINVOKE' threw an exception. ---> System.TypeInitializationException: The type initializer for 'SWIGExceptionHelper' threw an exception. ---> System.DllNotFoundException: FirebaseCppApp-8_9_0
   at (wrapper managed-to-native) Firebase.AppUtilPINVOKE+SWIGExceptionHelper.SWIGRegisterExceptionCallbacks_AppUtil(Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate)
   at Firebase.AppUtilPINVOKE+SWIGExceptionHelper..cctor () [0x000ee] in <5832818f1ad84593aa2717f5b3d23851>:0
    --- End of inner exception stack trace ---
   at (wrapper managed-to-native) System.Object.__icall_wrapper_mono_generic_class_init(intptr)
   at Firebase.AppUtilPINVOKE..cctor () [0x00000] in <5832818f1ad84593aa2717f5b3d23851>:0
    --- End of inner exception stack trace ---
   at Firebase.AppUtil.SetLogFunction (Firebase.LogUtil+LogMessageDelegate arg0) [0x00000] in <5832818f1ad84593aa2717f5b3d23851>:0
   at Firebase.LogUtil..ctor () [0x0001e] in <5832818f1ad84593aa2717f5b3d23851>:0
   at Firebase.LogUtil..cctor () [0x00010] in <5832818f1ad84593aa2717f5b3d23851>:0
    --- End of inner exception stack trace ---
   at Firebase.FirebaseApp..cctor () [0x0004a] in <5832818f1ad84593aa2717f5b3d23851>:0
    --- End of inner exception stack trace ---
   at Framework.Core.Managers.FirebaseInstaller+<Initialize>d__6.MoveNext () [0x0001e] in <98c85913016548029f68f9361c660fef>:0
 Waiting for managers.
 Uploading Crash Report
 DllNotFoundException: FirebaseCppApp-8_9_0
   at (wrapper managed-to-native) Firebase.AppUtilPINVOKE+SWIGExceptionHelper.SWIGRegisterExceptionCallbacks_AppUtil(Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate,Firebase.AppUtilPINVOKE/SWIGExceptionHelper/ExceptionDelegate)
   at Firebase.AppUtilPINVOKE+SWIGExceptionHelper..cctor () [0x000ee] in <5832818f1ad84593aa2717f5b3d23851>:0
 Rethrow as TypeInitializationException: The type initializer for 'SWIGExceptionHelper' threw an exception.
   at (wrapper managed-to-native) System.Object.__icall_wrapper_mono_generic_class_init(intptr)
   at Firebase.AppUtilPINVOKE..cctor () [0x00000] in <5832818f1ad84593aa2717f5b3d23851>:0
 Rethrow as TypeInitializationException: The type initializer for 'Firebase.AppUtilPINVOKE' threw an exception.
   at Firebase.AppUtil.SetLogFunction (Firebase.LogUtil+LogMessageDelegate arg0) [0x00000] in <5832818f1ad84593aa2717f5b3d23851>:0
   at Firebase.LogUtil..ctor () [0x0001e] in <5832818f1ad84593aa2717f5b3d23851>:0
   at Firebase.LogUtil..cctor () [0x00010] in <5832818f1ad84593aa2717f5b3d23851>:0
 Rethrow as TypeInitializationException: The type initializer for 'Firebase.LogUtil' threw an exception.
   at Firebase.FirebaseApp..cctor () [0x0004a] in <5832818f1ad84593aa2717f5b3d23851>:0
 Rethrow as TypeInitializationException: The type initializer for 'Firebase.FirebaseApp' threw an exception.
   at Framework.Core.Managers.FirebaseInstaller+<Initialize>d__6.MoveNext () [0x000d2] in <98c85913016548029f68f9361c660fef>:0
 --- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <695d1cc93cca45069c528c15c9fdd749>:0
   at System.Runtime.CompilerServices.AsyncMethodBuilderCore+<>c.<ThrowAsync>b__6_0 (System.Object state) [0x00000] in <695d1cc93cca45069c528c15c9fdd749>:0
   at UnityEngine.UnitySynchronizationContext+WorkRequest.Invoke () [0x00002] in <a3bf785675754762a66d8639375071d6>:0
 UnityEngine.DebugLogHandler:Internal_LogException(Exception, Object)
 UnityEngine.DebugLogHandler:LogException(Exception, Object)
 UnityEngine.Logger:LogException(Exception, Object)
 UnityEngine.Debug:LogException(Exception)
 UnityEngine.WorkRequest:Invoke()
 UnityEngine.UnitySynchronizationContext:Exec()
 UnityEngine.UnitySynchronizationContext:ExecuteTasks()

Details:

• full log

• Firebase .so files are in the build in the server_Data/Plugins directory

• using .NET 4.x and unity 2020.3.31f1 -the server fails and crashes with this when built with mono or il2cpp backend

• this happens on AWS GameLift instances - https://aws.amazon.com/amazon-linux-ami/2018.03-release-notes/ (only info I found)

• this doesn't happen on Ubuntu 20.04.3 LTS (our test server), runs as expected

• this doesn't happen when we build for Windows platform, runs as expected.