Tested in 4.27.2 binary which produced 32 bit depth pngs in both the editor and PIE.
Using the HighResShot command to get a png while playing in editor results in a 24 bit depth screenshot where previously it was 32 bit.
Bit Depth should be 32, and roughly 400 KB in Size
Bit Depth is 24 bits, and less than 25 KB in Size
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-144280 in the post.