OpenGL Errors using ActiViz for Unity

Hi all. I’ve a fair bit of experience using Activiz 7.1.1 and separately with Unity3D and now looking at using the Unity3D plugin. I’ve downloaded the Medical Viewer sample package and also have a trial of the full plugin. Despite following the instructions carefully, testing on Unity 2018, 2019 and 2020 is giving me:

OPENGL NATIVE PLUG-IN ERROR: GL_INVALID_OPERATION: Operation illegal in current state
0x00007FF6A1CD36FC (Unity) StackWalker::GetCurrentCallstack
0x00007FF6A1CD7721 (Unity) StackWalker::ShowCallstack
0x00007FF6A2F4DBC5 (Unity) GetStacktrace
0x00007FF6A3DF628E (Unity) DebugStringToFile
0x00007FF6A0C09967 (Unity) LogGLES
0x00007FF6A0C07A81 (Unity) CheckErrorGLES
0x00007FF6A0C0EC09 (Unity) GfxDeviceGLES::AfterPluginRender
0x00007FF6A3AF6690 (Unity) GfxDeviceWorker::RunCommand
0x00007FF6A3AFE03C (Unity) GfxDeviceWorker::RunExt
0x00007FF6A3AFE428 (Unity) GfxDeviceWorker::RunGfxDeviceWorker
0x00007FF6A19B96E0 (Unity) Thread::RunThreadWrapper
0x00007FFE8E467C24 (KERNEL32) BaseThreadInitThunk
0x00007FFE8F76CEA1 (ntdll) RtlUserThreadStart

I see a similar closed topic at: How to integrate VTK with Unity but there was never a solution posted that I can see.

Many thanks in advance.