After upgrade from 2019.04 to 2020.02 I have noticed my agents will not upgrade when initiated from the Manage Agents area. They stay indefinitely in the Upgrade in Progress state and never come out of it. At the target I don't see any events or logs indicating the upgrade of the agent is even being attempted. Installing the agent manually resolves.
I see mention here of an issue here that indicates a certificate issue but it vague.