Spawn scene object not found for 1

I'm working on a multiplayer project with UNET and running into a problem that hasn't occurred before. The host creates a room and everything looks fine, but when a client connects, certain objects are disabled in the hierarchy and I get these cryptic errors below:

 Spawn scene object not found for 1
 UnityEngine.Networking.NetworkIdentity:UNetStaticUpdate()
 
 Spawn scene object not found for 2
 UnityEngine.Networking.NetworkIdentity:UNetStaticUpdate()
 
 Failed to spawn server object, assetId=7ae8c0425a9fe524b89e6a8370ce629a netId=4
 UnityEngine.Networking.NetworkIdentity:UNetStaticUpdate()
 
 Failed to spawn server object, assetId=7ae8c0425a9fe524b89e6a8370ce629a netId=5
 UnityEngine.Networking.NetworkIdentity:UNetStaticUpdate()

I'm not sure what's going on, since I've done a similar thing before and when the client connects I don't get this issue. After some research I found some people fixed this by removing and reading the NetworkIdentity component from their prefabs, but that hasn't worked for me.

I'm using Unity 5.5.2 btw.