Crashed when upgrading

Issue: (quick one-line precis of what happened)
Crashed when upgrading.
Crash (y/n): (did the game crash?)
Y
Platform (Windows/Mac/Linux): (what sort of computer were you playing on?)
Win10
Version number: (what version number of the game are you running? If you’re able to reach the ‘desktop’ interface of the game, you can see this information in the ‘About’ window)
18.50
Description: (more detailed description of what happened, if you need more space. If whatever happened happens repeatably, please let me know!)

Went to upgrade from 6.4.100 to 6.5.0 and crashed when hitting accept… Over 2000 logged in

(please consider attaching your save file, if you think it might help me track down the trouble you’re having!)