This is now fixed in the latest packages on GitHub…
Download and checked, super 
also fancy sidecar detected dialog 
True, loading of .CUBE LUTs is not fast, but only happens once the first time the LUT is accessed. Then it should go much faster…
is there a size of LUT that loads faster, or any other more suitable format 3dl, mga, look, png, etc.?
Could you provide me an example of .PFI file where this happens? I could not reproduce this problem myself.
I think I know what was going on, I loaded a couple images and tried to mix them… it seems PhF always uses the background img (say first image loaded) as BKG or bottom layer; am I right, can I make BKG a “normal” layert? Probably that’s the logic behind gradients not working on the BKG layer and mix happening even in momentarily BKG on top. At least now I understand the “kid”, h eh e