Generally you get trapped if the output is blocked which interferes with item spoilage that's used as a trigger to respawn the player. Until the spoilage mechanic is updated (or I use a completely different approach which tbh is a bit tempting) this is just an unfortunate bug that I can't reasonably fix.
Edit for more information:
While there are some checks for this when attempting to enter the recycler, if the output is blocked after the fact (e.g. an item on a belt moves onto the output of the recycler) then the player will be stuck forever.
A respawn button is planned in a future update as a secondary fail-safe.