The .pak files gets mounted, and along with them is the .utoc files for those files.
.ucas files need not be mounted, it’s being referred through those .utoc and .pak files.
It gets mounted, after I checked the source code a bit.
But even if there is no change in the content, every build has a bit different size of .pak, .utoc and .ucas files. I don’t know why, but it’s observed.