Problem is still unresolved. Until a final solution I suggest not buying EAP 110 outdoor v3. In makes a lot of trouble.

For the reader: Problem still exists. Until finally solved I recommend not buying EAP-110 outdoor v3. It causes me a lot of trouble and connection issues.

For the readers with same problem: TP-Link provided me with a beta firmware, which is not perfect, but far better than the latest firmware. So hopefully there is soon an official release.

So we're still solving the trouble. With ssh access the problem could be traced down via dmesg. ACKTIMEOUT call ath_internal_reset begin leads to a connection drop. Still figuring out if...

@Connectionloss It seems the more SSIDs and the more clients are connected to an AP, the more often the connection problems occur. On the test AP I habe one connection drop within the last 11 hours....

I did a soft reset and added one SSID by one except that one with an access control rule, because I didn't see an option for access control rules in standalone mode. There are no connection drops...