I might have a different problem, but my investigation has led me to textures and DDC.
I’m using virtual textures, and in some random cases, textures become different: the material displays other textures instead, and on the game map, the material appears completely different.
And the funniest thing is that when migrating my working project from 5.5 to 5.6, I either get materials with the wrong textures (they can be temporarily restored by reopening the textures), or a bunch of different errors, for example:
Assertion failed: RecordTypeBaseOffset + SegmentIndex * 2 + 2 <= NumRecords
EXCEPTION_ACCESS_VIOLATION reading address 0xffffffffffffffff (and other variations)
Assertion failed: SingleShaderBindings.ParameterMapInfo.TextureSamplers.Num() == 0
Crash in runnable thread RHIThread
…often in modules like:
UnrealEditor-Renderer.dll
UnrealEditor-RHI.dll
UnrealEditor-D3D12RHI.dll
I can’t reproduce the problem reliably/stably.
However, projects created directly in 5.6 don’t seem to have these problems (I’m not entirely sure). But all my projects migrated from 5.5 have various problems with materials, even if the projects were almost identical at different stages.
It seems I’ll have to revert back to 5.5, at least because of reflections (we have Nanite, but the reflections look like broken geometry and have AO artifacts. We have to disable nanite, lose performance but get high-quality reflections).
Overall, it’s a massive pile of issues that look like a tangled knot of nodes.