In Beyond 23, currently on the 'rank up Crab nebula x2 + (????) [Oort cloud object]' mission that unlocks 'Crab Pulsar'
Had left the game open overnight while I was asleep (since offline is only 32% gain) to let the previous 'beyond 22' producers (Hourglass, Cats's eye, etc) run so that I could afford the missions to unlock the new '23' producers.
After coming back to the game, I was able to open several new producers and finish several additional missions and continue to play normally for 30 mins. Let the game AFK again for an hour or so while I took care of some other things. When I came back, I wanted to cash in my offline progress in other modes, so I started with Mesozoic, the loading stalled for several seconds. I switched to task manager to kill the thread when I noticed the RAM spike and the fact that it was still growing.
I let it run for another minute or so to see if it would kill itself, but it didn't. So I 'X'ed out the window manually with the mouse (was surprised that actually worked).
I tried to reproduce the error by logging back in, going to Beyond then attempting to open Mesozoic, but it loaded Mesozoic again with no additional issue.
Started at ~12GB RAM used, you can see from the screen capture that RAM growth wasn't going to stop anytime soon and had already started blowing up the pagefile as well.
v 29_58 on Steam™