I hit an example of RetroPie+RetroArch locking my Pi today using lr_mame with an out-of-date ROM. I could not find any way to get local access to a command prompt using either the controller or my keyboard. (Tried Ctrl+Alt+F2 and Select+Start)
so the thing to note here is lr-mame is in the 'experimental' section of the retropie package manager. experiments fail :P
to elaborate on this, there's a process to getting a particular version of MAME/FBN into a libretro (lr-) core, and it's quite difficult because of their vast complex code bases. to that end, many of the lr-mame* and lr-fb* cores are unfinished and/or abandoned cores at various stages of functionality. they crash, they don't control right, and so on.
hence the reason we recommend specific versions of mame/fbn here is not just because they're the most performant/compatible for the hardware, but because those listed cores are actively developed and function properly.
So again, those could indeed just be roms that just aren't designed to work w/lr-mame (on the site I usually DL from, I saw there were versions labeled plain "MAME," however both links were dead),
appreciate you're trying to learn but if you continue to follow this approach you will continue to make what is a very simple two step process into a nightmare for yourself. even if one of your random downloads with a randomly selected version of MAME, for my above reasons you may be using an unrecommended core.
Unless I missed it, is there one of those numbers that is associated/optimized to work w/FB? I assume if I search on here, I can also find how to upgrade my version of Final Burn? (since most of the packages seem to be versions of MAME, and someone on another post suggested that my version of FB may be out of date...)
FB Neo v0.2.97.44-WIP
note this is a subset of the current mame version and will eventually change if you update it (so don't update it if you prefer)