You might encounter the following error while registering a new server in PG Admin.

Instance '<Server at <guid>>' is not persisted.

The issue is mostly due to uninstalling and re-installing PG Admin or installing a different version of PG Admin.

The resolution would be the following.

• Close PGAdmin
• Browse to C:\Users\<your user>\AppData\Roaming
• Delete the folder PGAdmin
• Open PGAdmin

This will resolve the issue