Lync 2013 Response Group Offering in the Wrong Order

The scenario is this: You’ve got a serial response group configured with Lync 2013. Even though the first user in the response group is available and waiting for a call, the call isn’t offered to them first. It’s like they’re invisible, like a vampire in the mirror, like me in front of a faucet with a motion sensor. You can move them up or down, rebuild the group, it doesn’t matter, the problem comes back. You’re at the latest patch level too. I’ve seen this a few times. I haven’t had a chance to fully work it out because before I get too far a simple service restart makes the problem go away. We’ve been problem free at a client who had this issue for three months now (edit: now six as of June). Here’s hoping the next time this crops up we have time for a fun deep dive!