Per Licensee:

Since we switched to DX12 we started to see strange behavior in material previews. I was able to reproduce the problem in UE 4.19 vanilla as well.

We usually have to force recompiling the shaders to fix the issue. I was unable to reproduce this bug using previous version of DX

See attached video. I have reproduced this issue in 4.18.3 and 4.19.2.

Steps to Reproduce
  1. Open new project with DX12
  2. Create a new material as shown in attached screenshot
  3. Start previewing nodes along the top of the graph (TexCoord, Rotator, SphereMask, 1-X)

Result: After previewing nodes a few times each, the preview will start to behave unexpectedly. TexCoord preview might show SphereMask result, 1-X node preview might show TexCoord result or Rotator result, etc.

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Affects Versions4.
Target Fix4.22
CreatedMay 16, 2018
UpdatedNov 2, 2018