Awesome. I came back here to reply, as I had gotten a proper UDN response on this. It is a known issue that already has a fix in UE GitHub if you have access to that.
And yeah, the suggested work around was to just nuke Synchronized keys as you say for now, as that is what is ultimately causing this issue. Just doing that was fine for me as I had only 1 sync key and I was no longer even using it. But I imagine if you need them right now, you will want to get that fix!