Upgrade from 2.26.0 -> 2.27.0 UI panel is stuck with Some GRPC Errors

While upgrading PMM Server from 2.26.0 -> 2.27.0 for both long-running QA instances, we faced a weird issue on the UI, we had this GRPS error with the Update-status endpoint consistently failing.

When I look at the upgrade logs, inside /srv/logs/pmm-update-perform.logs it seems all was fine, there isn't any failed task, but the UI was not changing at all.

Checking the status of the Upgrade process, it was exited and not running, logs seemed fine, the UI was upgraded to 2.27.0 and the instances were still being monitored. 

STR:

1) Have a long-running PMM-Server 2.26.0 instance, (in our case we had like one instance running for 1+ year and other for 6+ months)

2) Upgrade via UI to 2.27.0

3) See the GRPC error, (not sure what better way to reproduce this for a fresh instance)

User Impact: The UI Upgrade stuck could cause panic

here is the link for upgradelog file