[colburnmh]

A few ideas to consider:

Do you mandate working tests and reasonable test coverage as part of your checkins? That could help, but it if you don't currently do that, productivity will drop further before it picks up. But that's the nature of any impactful change.

When there absurd back and forth on PRs, step-in and mediate a resolution. Pull the people into a room and require a resolution before anyone can leave--drastic, but soon people will realize that they pay more for pointless whinging. It's not doing the company any good for pointless bickering, and it's not improving the product either.

Considering using an external code-review as a service like PullRequest while you are gone. And maybe keep them if it works well.