I dont use RPI’s… but… I assume it would be the same… Theres an easy downgrade path, which is the following. Its pretty much all automatic with this.
sudo apt -y --allow-downgrades -y install openhab2=2.5.2-1
Though I would clear the cache and reboot after
so if you wanted to see if that was the issue or not, this should be a quick easy way to check.
P.S. Openhab will take a little longer to start on first boot after that, just like if you had performed and upgrade, but should all be working withing 3-5 minutes of a reboot/startup.