MySQL/PostgreSQL/MongoDB Instance Summary and Node Summary dashboards: PT Summary Panel broken after upgrade

We have a new bug introduced, PT summary panel is broken post-upgrade, upgrade tests started failing on this. 

Steps to recreate:

1) Setup PMM 2.19.0 or older

2) Enable Experimental Repo

3) Check PT summary panel on Node Summary Dashboard for pmm-server post-upgrade.

Impact on User: Broken PT summary Panel

QA: Please check other PT-related panels, if they are also broken post-upgrade.