Unmet requirements: env.AAAA exists

Hi,

After updating to the latest TeamCity (2021.2 build 99542), our Rspec tasks (Ruby on Rails tests) no longer run. The problem is no agents are compatible because of this env var missing: env.AAAA

After some digging, this is caused by the Build Feature: Ruby environment configurator -- if I disable it, requirement disappears. 

The strange thing is I didn't change any of the configurations, environment, rvm setup or anything except updating the TC so I suspect it's a bug somewhere. This variable is not defined anywhere, nor have we ever used, so I'm a bit lost.

Any suggestions?!