Unity 2019.3.12 Namespace not found & unable to update assemblies

Hi all!

We have been creating a game in Unity 2019.3 (ranging from 4f, 5f & 10f) and today I updated to 2019.3.12f.
During the update process and I got the following errors:

1.
Unable to update following assemblies:Assets/Third Party Assets/Photon/PhotonLibs/Photon3Unity3D.dll (Name = Photon3Unity3D, Error = 131) (Output: C:\Users\Xform\AppData\Local\Temp\tmp42998811.tmp)

System.InvalidOperationException: Operation is not valid due to the current state of the object.
at Mono.Cecil.ModuleDefinition.ReadSymbols (Mono.Cecil.Cil.ISymbolReader reader) [0x0002f] in <a3989f8c34e6476eaca56644d5639ee8>:0
at Mono.Cecil.ModuleReader.ReadSymbols (Mono.Cecil.ModuleDefinition module, Mono.Cecil.ReaderParameters parameters) [0x0004a] in <a3989f8c34e6476eaca56644d5639ee8>:0
at Mono.Cecil.ModuleReader.CreateModule (Mono.Cecil.PE.Image image, Mono.Cecil.ReaderParameters parameters) [0x00081] in <a3989f8c34e6476eaca56644d5639ee8>:0
at Mono.Cecil.ModuleDefinition.ReadModule (Mono.Disposable`1[T] stream, System.String fileName, Mono.Cecil.ReaderParameters parameters) [0x0000d] in <a3989f8c34e6476eaca56644d5639ee8>:0
at Mono.Cecil.ModuleDefinition.ReadModule (System.String fileName, Mono.Cecil.ReaderParameters parameters) [0x0006c] in <a3989f8c34e6476eaca56644d5639ee8>:0
at Mono.Cecil.AssemblyDefinition.ReadAssembly (System.String fileName, Mono.Cecil.ReaderParameters parameters) [0x00000] in <a3989f8c34e6476eaca56644d5639ee8>:0
at AssemblyUpdater.Core.AssemblyUpdaterContext.ReadAssembly (System.String assemblyPath, APIUpdater.Framework.Log.IAPIUpdaterListener listener, System.IO.FileAccess mode, System.String[] searchPaths) [0x00084] in <3007858faa2c4f5e8f4c1005f142a37d>:0
at AssemblyUpdater.Core.AssemblyUpdaterContext.From (System.String assemblyPath, APIUpdater.Framework.Configuration.ConfigurationProvider configuration, System.String[] assemblySearchPaths, AssemblyUpdater.Core.UpdaterMode mode, APIUpdater.Framework.Log.IAPIUpdaterListener listener) [0x00025] in <3007858faa2c4f5e8f4c1005f142a37d>:0
at AssemblyUpdater.Core.AssemblyUpdaterContext.From (System.String assemblyPath, System.String[] assemblySearchPaths, AssemblyUpdater.Core.UpdaterMode mode, APIUpdater.Framework.Log.IAPIUpdaterListener listener) [0x00001] in <3007858faa2c4f5e8f4c1005f142a37d>:0
at AssemblyUpdater.Application.Program+<>c__DisplayClass0_0.<Main>b__1 (AssemblyUpdater.Application.UpdateOptions o) [0x0001f] in <3007858faa2c4f5e8f4c1005f142a37d>:0
at CommandLine.ParserResultExtensions.WithParsed[T] (CommandLine.ParserResult`1[T] result, System.Action`1[T] action) [0x0001e] in <5f6458f0234f43a48c09047109c24684>:0
at AssemblyUpdater.Application.Program.Main (System.String[] args) [0x0004c] in <3007858faa2c4f5e8f4c1005f142a37d>:0
Following assemblies were successfully updated but due to the failed ones above they were ignored (not copied to the destination folder).Assets/Third Party Assets/Photon/PhotonLibs/Metro/Photon3Unity3D.dll (Result = 0) (Output: C:\Users\Xform\AppData\Local\Temp\tmp1dfd171e.tmp)


UnityEditor.Scripting.APIUpdaterLogger:WriteErrorToConsole(String, Object[])
UnityEditorInternal.APIUpdating.APIUpdaterManager:HandleAssemblyUpdaterErrors(IEnumerable`1)
UnityEditorInternal.APIUpdating.APIUpdaterManager:UpdateAssemblies()
UnityEditorInternal.APIUpdating.APIUpdaterManager:ProcessImportedAssemblies(String[])

2. (This one has been reported in another thread as well)
Assertion failed on expression: 'gForceReimports->empty()'


The game however does start and work.
However in VS 2017 I am getting namespace not found errors. Funnily enough I can run & build the game just fine. Unfortunately I can't navigate or use intellisense on anything PUN related. I have had a similar issues like this before on another system which could be fixed by removing the .vs folder (and more specifically the .suo file in there). This way stuff gets rebuild and it was working again. This does not work for me anymore (Win10).

Anyone with similar issues? Anyone who can help me out?

Pieter