Within the same job, we started getting different arch values for parallel runs

So we use arch as a key to cache ruby gems between jobs/steps.

Within same job, some of the parallel runs are starting to get arch = arch1-linux-amd64-6_106

Checking back a couple of days ago, we were consistently getting: arch1-linux-amd64-6_85

Is there a reason these would vary between parallel runs on the same job or workflow? or is this a bug?