The AP was able to reach the controller without any issues (from Switch Perspective).
It is a 1Gbit/s cabled Network.
No other Devices on this Switch had any issues. I am monitoring the reachability of my controller and all of my Switches. No Outage. They had no issues. There where no connectivity Problems to the Controller. All other APs also had no connectity issues.
After i found the problematic Switch Port with the AP attached i disabled the Port. The Network was stable again. After enabling the Port, Network Problems came back again.
Disabling or Enabling the Switch Port did not changed the Mesh Mode of the AP.
APs was listed still as a Mesh-AP within my ZD GUI.
After restarting the AP the AP was listed as Root-AP again and my issues were gone.
Sure i think the Switch Port had an Problem. There must be a Reason, why the Port was offline for about 20 Seconds. This is because the AP looked for an alternative Route.
But the AP did not changed his Mesh State after the Port was online again. Disabling/Enabling the Port did also solve nothing. Only the Restart of the AP solved my issue.
So i asked me if this behavior is a bug, by design or just a faulty configuration from my side. I thought AP should switch to Root-AP Mode back if the Network Connection is restored.
Maybe there are things like Reccomendation using Manual Mesh Settings, Disabling RSTP on Switch, Known Bug, etc.