It seems all attempts to upgrade agent packages via Package Manager now result in "Installing" and en eventual timeout.
When I run a configuration poll afterwards, the agents were upgraded successfully - but with the number of agents we are running, deployment is slowed down quite a bit as I have to upgrade in small batches rather than just queuing everything.

All our agents are using Agent Tunnels, so I am not sure if that is somehow related?

Cheers

Update: A single agent which was not using Agent Tunnels actually completed the upgrade properly.