Character stuck in map after Ilum cutscene

FWIW, I found this post when googling for the answer to what (at first) appeared to be the same issue.  However, after a bit of trial + error, I managed to figure out what to do to get past this.  At least in my case, it *appeared* that I was trapped under the ice for about 5 mins but after some experimentation I discovered that if you submerge (swim down) sufficiently far its possible to find an underwater tunnel out from under the ice.

So in my case, it wasn't a bug as much as just a poor design of the game providing little ability for me to understand where/how to escape from under the ice  -- the ice obscures the view of the light from below that 'hints' that the tunnel is down there to find and the murkiness of looking at Cal through the ice further makes it very hard to even align Cal to up vs down under the water.  I solved it by aggressively hitting the 'swim down' button (right mouse on PC) until I got far enough away from the layer of ice that the 'chase camera view' of Cal from behind let me see that I was indeed moving forward/deeper in the water.

Not sure if this will also solve your issue (your issue may indeed be a real bug), but since it took me 5+ mins of fooling around under the ice to realize there was a way out way at the bottom, I figured I'd offer to anyone else that what may at first appear to be a bug may well not be.  Hopefully this advice helps others too.