I agree that it is very strange and quite possibly unrelated. I know I rebooted my phone several times because that seems to be pretty much the first step to debugging these annoying Bluetooth issues. Only after I noticed that my Weber grill thermometer was also unable to get a connection going did I start to suspect some system-level software update that got installed because I knew the thermometer worked in early December. And yes, that one also started working again after the reboot.
This is a link to the post (by Mike Zalansky) that pointed the finger at the ARCore update. https://productforums.google.com/d/msg/phone-by-google/-lpPfDGvkNw/ywUcLkg-CQAJ
Except for the two emails following up on the one above, the rest of that thread is pretty much useless. But you may very well be correct and the uninstall/reboot cycle just happened to unwedge the BLE stack at the right time for me.