I'm happy to announce that, starting today, OGF tile rendering runs on a separate server. Hopefully, this will positively affect application performance.
It also means that JOSM users need to adapt their imagery preferences, as described here:
Note that this applies only to the "Imagery preferences". The "Connection settings" for API access remain as they are.
To ensure a smooth transition process, the tile rendering on the old server will remain enabled for the next few days, but expect it to be switched off in the near future.