While testing Scummvm 2.5.0 I bumped into this issue too --- seems to be specific as said here to lr-scummvm's interaction with RetroArch as loading titles explicitly with the non-lr version of ScummVm works.
Not sure exactly when this broke, but my RPi3B downstairs works fine on RetroArch 1.8.8 and my 4B on 1.9.7 doesn't work. Tomorrow I'll try to upgrade my 3B to the latest lr-scummvm just to see if it still works, just because I'm curious.
Anyone else hitting this, and have a way to work around without downgrading? Lr-Scummvm is much better for input. It might be tracked here:SupervisedThinking created this issue in libretro/scummvm open [Bug] SCUMMVM hangs on boot / freezes RA #183