First playtest of Chernobyl Freeplay ended in a crash about two in-game days in when I tried going into X-18. Also crashed every time I tried to load my saves after that. The log reads:
>[error][ 87] : The parameter is incorrect.
In my experience this error is somehow related to the optional tasks. In the old CF I got this error when I added too many tasks. I didn't add so many tasks this time around but I did have more than one task active when I entered X-18. Maybe I accepted one too many and corrupted my saves by saving with more than one task active.

Could also be a memory issue. The Zone was pretty hectic during the first playtest. There were gunfights and mutants running wild in pretty much every level. I'm making changes to lessen the load on the game for my next playtest. Gonna try not having more than one task active at a time as well.