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.
Expected Results:
Bit Depth should be 32, and roughly 400 KB in Size
Actual Results:
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.