Rockbox

This has happened with at least the last two builds, but I do not recall this behavior in any previous build.

If I skip ahead a few songs, doing the whole "Nope, Nope, Next..." it eventually will fail to start playing, staying at 0:00.
When the player reaches this state, you can continue to skip to the next or previous songs without incident. If hit the power button (which normally would stop playback and return to main menu) it remains at the current song (still at 0:00 since playback has failed at this point) but you cannot skip tracks anymore. If you let it sit, the screensaver turns off the backlight. Any keypress will turn the backlight back on, but the player does not respond in any other fashion. This state persists until you use the power switch to hard-power off the player.

If instead of just tapping the power button, I hold it, the player will turn off after playback has failed, but if tapped first, the player will not turn off.

Once this happened early into a drive, so instead of searching for the switch, I let the player sit. After about 15min it returned to normal operation, responding to every keypress that had occurred while it was ignoring me.