My thoughts were that they would transfer prisoners between facilities, but trump up some charges during the transfer under PORD. They'd then have new charges with longer sentences & be sent to a different facility. If he or she weren't known there, then their word wouldn't be that trustworthy.
This instance, something went wrong & a prisoner was just moved from one floor to another so no cover story was going to fly.
"We were just about to put him on a transport and, the Emperor as my witness, dude totally lifted a cargo crate near the shuttle. Total Jedi stuff. So back to jail."
Someone translated the charges for Cassian during his sentencing and one of the charges said something like "possible Force user" or something along those lines. So it's entirely possible they just tack that on to get a bigger sentence.