My terraria went through this weird stage when I had tAPI. After I played a bit with my character, when I turned my computer off all my data on tAPI was erased. When I put the old files before my character/world files were erased, in the character selection screen where it should say my characters name it was completely blank. When I loaded my world save (which was not blank and normal), I crashed.
MODS:
Thorium+
TUWM
Dark Souls weapons
Ulterria
EDIT: Not sure but this was in my logs:
Ionic.Zip.ZipException: Cannot read that as a ZipFile
at Ionic.Zip.ZipFile.ReadIntoInstance(Ionic.Zip.ZipFile zf)
at Ionic.Zip.ZipFile.Read(System.String fileName, System.IO.TextWriter statusMessageWriter, System.Text.Encoding encoding, System.EventHandler`1[[Ionic.Zip.ReadProgressEventArgs, Ionic.Zip.Reduced, Version=1.9.1.9000, Culture=neutral, PublicKeyToken=null]] readProgress)
at Terraria.WorldFile.ActualLoadWorld(System.String world)
at Terraria.WorldFile.loadWorld()
at Terraria.WorldGen.playWorldCallBack(System.Object threadContext)
at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(System.Object state)
at System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, System.Object state, System.Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, System.Object state, System.Boolean preserveSyncCtx)
at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
at System.Threading.ThreadPoolWorkQueue.Dispatch()
at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()
Ionic.Zip.BadReadException: Bad signature (0x00000066) at position 0x00000000
at Ionic.Zip.ZipEntry.ReadHeader(Ionic.Zip.ZipEntry ze, System.Text.Encoding defaultEncoding)
at Ionic.Zip.ZipEntry.ReadEntry(Ionic.Zip.ZipContainer zc, System.Boolean first)
at Ionic.Zip.ZipFile.ReadIntoInstance_Orig(Ionic.Zip.ZipFile zf)
at Ionic.Zip.ZipFile.ReadIntoInstance(Ionic.Zip.ZipFile zf)