Sorry about this! We did a series of builds in rapid succession that created incompatibilities with robots created in previous builds. The fix is to edit the .RR2Bot files for the robots.
You can find a complete description and how to fix the broken .RR2Bot files on the GameTechMods website. I promise the fix isn't too painful, and feel free to ask if you have questions!
Here's the link to the fix:
https://gametechmods.com/forums/robot-rumble-2-0/rr2-the-case-of-the-missing-rob...
If you are interested, here's a link to a more complete discussion:
https://gametechmods.com/forums/robot-rumble-2-0/robot-rumble-2-0-robot-combat-s...