Alpha channel missing on import — packed RGBA mask from Substance Painter

Development World Creation
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Summary

I’m packing a four-channel mask in Substance Painter (latest) using User0–User3:

  • R — damage
  • G — weathering
  • B — dirt
  • A — paint mask

I built a custom export template that splits the output into R/G/B/A and assigned the four User channels to their respective slots. Exporting as either Targa or PNG, the resulting texture shows no alpha channel once imported into UE 5.8 — the Texture Editor reports no alpha and the material only gives me three usable channels.

Already tried:

  • Exporting as both TGA and PNG (8-bit)
  • Confirmed all four User channels exist in the texture set and contain painted data
  • Unchecked Compress Without Alpha
  • Set Compression to Masks (no sRGB), sRGB off

My questions:

  1. Is there anything in the export template setup that would silently drop the alpha assignment?
  2. Does UE strip the alpha channel on import if it reads as uniform, and is Force Alpha Channel the correct fix?
  3. For a mask with four independent channels, is BC7 the recommended compression over BC3 to avoid cross-channel bleed?

Any pointers appreciated — happy to post screenshots of the export template or the import settings if useful.