I've bought a GT AC2900 to upgrade my wifi network and am now using my RT AC88U as AiMesh node.
The system runs fine when started freshly, unfotunately the node goes offline within one or two days. Keeping it to wait for automatic reconnection didn't work. The mobile app cannot restart the node as well - the command cannot be transmitted. The only way to "reactivate" the node is to switch it off an on again - daily. Very annoying!!
The firmware of both devices is the latest possible but the problem persists. I tried to use the two the other way around - with AC88U as router ant teh AC2900 as node ends up with the same problem. I tried some hints found in different websites/forums but no improvements yet. Some of the things I tried so far: dectivating DHCP deactivating "Universal Beamforming" deactivating "Airtime Fairness" switching off the 2,4 or 5GHz band factory resseting several times