Comment 9 for bug 1585641

that CI test did eventually hit the error, so that means it's probably not a commit in Ironic. Focusing in on the commits in Nova, it looks like this might be the problem:
https://review.openstack.org/#/c/306670/

as that change in behavior corresponds exactly with what I'm seeing in the job logs: some nodes usually start reporting memory_mb=0 and memory_mb_used=0 making them unavailable for scheduling from the RamFilter's perspective even though no instances are assigned to them.

going to try the CI test again with the downgraded nova package and see if I'm able to reproduce.