There's no trap or anything. You can just jetpack your way out of it.

POI has a corridor with corrosive gas and a small opening at the end. You enter it and go down a ramp, and then you get locked in. I couldn't go forward through a small tunnel or go back the same way. I was forced to turn on god mode to get out.

Nothing would lock you in, but you may have to jump or use your jetpack to get out.

FYI I had a similar scenario but I think it may have been a vent. Normally I just drop down into the lava area but once there I found a path leading somewhere so I followed it. It eventually it lead to a tunnel I had to crouch in that then dropped into a larger room. Both exits from the room required me to “jump crouch”, ie jump about 3 ft up and in mid air crouch to get back in the tunnel. I couldn’t do it (not sure if it’s possible). I tried for about 30 min until I used god mode to free myself. I guess spelunking can really be dangerous! :)