Decals fading in with Fade Duration set to zero.
Found in 4.21 CL# 4753647, 4.22 CL# 7053642, 4.23 Preview 5 CL# 7838574
The decal will fade in even with no fade set
The decal would not fade in
Set the Fade Duration to 0.01 and the decal will no longer fade in
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-78628 in the post.