Vulkan Frame Dropping

I wonder if anyone could help diagnose my issue. Apologies if this is not the right place for my problem.

I have a game capped at 30fps that drops to ~15 fps like clockwork. Usually the game will start up fine but after a short while will start skipping. I've tried to diagonose the issue with the profiler but can't seem to find any smoking guns. It is a standalone windows game. Interestingly if I build the game with DirectX 11 it will run at consistently at around 20fps with no spikes at all. The game uses almost all vram which could be the issue but I think I get a similar problem on machines with more vram than mine.

There is also an intermittent crash that also has no particular cause or warning and again I'm unsure if this is related. See crash logs below.

 UnityPlayer.dll caused an Access Violation (0xc0000005)
   in module UnityPlayer.dll at 0023:6b0a4ff1.

...

 Stack Trace of Crashed Thread 18680:
 ERROR: SymGetSymFromAddr64, GetLastError: 'Attempt to access invalid address.' (Address: 6B0A4FF1)
 0x6B0A4FF1 (UnityPlayer) (function-name not available)
 ERROR: SymGetSymFromAddr64, GetLastError: 'Attempt to access invalid address.' (Address: 6B0A64D5)
 0x6B0A64D5 (UnityPlayer) (function-name not available)
 ERROR: SymGetSymFromAddr64, GetLastError: 'Attempt to access invalid address.' (Address: 6B07A4F7)
 0x6B07A4F7 (UnityPlayer) (function-name not available)
 ERROR: SymGetSymFromAddr64, GetLastError: 'Attempt to access invalid address.' (Address: 6B173649)
 0x6B173649 (UnityPlayer) (function-name not available)
 ERROR: SymGetSymFromAddr64, GetLastError: 'Attempt to access invalid address.' (Address: 6B17556D)
 0x6B17556D (UnityPlayer) (function-name not available)
 ERROR: SymGetSymFromAddr64, GetLastError: 'Attempt to access invalid address.' (Address: 6B175642)
 0x6B175642 (UnityPlayer) (function-name not available)
 0x6B917FF8 (UnityPlayer) UnityMain
 0x7703FA29 (KERNEL32) BaseThreadInitThunk
 0x77B67A4E (ntdll) RtlGetAppContainerNamedObjectPath
 0x77B67A1E (ntdll) RtlGetAppContainerNamedObjectPath

Most other threads seems to be stuck at

 ZwWaitForSingleObject

If you need any other details let me know.

Thanks,

Adam