Thanks, @pturmel. We should have very few (manual) tag reconfigurations, but it's possible a poorly written UDT upgrade script is hanging around. We do have some frequently updated Memory tags. However, it seems there must be another factor as I can take a manual backup from the same gateways to the same locations in seconds (or up to a few minutes for some on slower networks) via the web interface in a browser running on the gateway. However, if gateway already has blocked scheduled backup threads as shown below, I have to either wait for these to clear or restart the gateway to clear these before I can take a quick manual backup.
Some more info: Ignition 8.1.44 gateway is not heavily loaded.
The two blocked threads are scheduled backups.
The scheduled backups generally complete eventually, but take a long time. For example, one gateway just completed a 10.6 MB scheduled backup in 3.5 hours.