With a specific combination of resource packs (likely a PBR one and another that alters the banner/banner pattern textures) banners will display a random banner pattern of their base colour while the rest of the banner remains black. I have tested this with both Kelly's RTX https://mcpedl.com/kellys-minecraft-vanilla-rtx-conversion-pack/ and my own PBR resource pack.
Steps to Reproduce:
Open a world with Ray Tracing on and with the two resource packs linked below applied to global resources.
Place and view a banner of any colour.
Observed Results:
The banners display a Snout banner pattern in the colour of their base colour, and the rest of the banner is completely black.
Expected Results:
The banners should retain the same functionality they had before applying the second non-PBR resource pack, as in displaying their base colour without any banner pattern (as there are none applied).
Global Resources:
[media]Defined PBR: https://www.mediafire.com/file/xnr66e9foxfcoi5/Defined_PBR_v1.1.4.mcpack/file
MultiPixel: https://www.mediafire.com/file/g890rxv9yg4epad/MultiPixel_Bedrock_1.17_rv1.mcpack/file
I don't believe that a random pattern with RTX, but only displays the background color.