You should review your installation.
My install notes.
OE
Having little time to tweak and mainly following Asuswrt-Merlin forum, I have missed this thread and wasted the family long weekend with what someone nicely called AiMess!
Just here to say thanks to OE for his notes.
Also many thanks to RMerlin for all the years of keeping us in the Asus bandwagon!
I went through a full reshuffle of my good old RT-AC5300 that has always been running the latest alpha/beta dirty flashed Merlin serving 80% of the house well, trying to add a GT-AC5300 as an AiMesh node to cover the 20% of the house where only 2.4G works.
So far, I've experienced just about everything mentioned by other frustrated users here - from simple FTP session between 2 of my laptops breaking and wouldn't reconnect because they bounced around the 2 routers.
To WiFi calls dropping all the time under AiMesh but used to work fine.
To the slow speeds because somehow 50-60 devices moved to the node.
To Google Cast insisting I've lost 8 of my Home speakers and I can't cast the next song to them.
To... well, just about everything that used to work better even with my older RT-AC68U (yeah, I tried adding it to the AiMesh around Christmas but it was a disaster and I had assumed it was too old, so went after another RT-AC5300 or GT-AC5300 or maybe some AX model).
Any ideas or I'm singing the same song as most of you in this thread?
Typing this after I completed OE notes from the link above now several times, currently with a fully reset GT-AC5300 as the main router (now with beta Firmware Version:9.0.0.4.384_81551), just one node RT-AC5300 (now also with RT-AC5300_9.0.0.4_384_81468-gcc98201.trx) and looking at the nearest Smart Display connecting, casting Spotify, it stopped, no wifi, reconnecting..., connecting... Spotify starting... and stopping again... no wifi...
Off to r/Vent and probably restoring Settings_RT-AC5300_384.15 and putting the GT-AC5300 back in the box to see if BestBuy would take it back after a month.
I wish I saw this thread a few weeks and $$$ earlier!