I have no issues with ethernet and 5ghz but good God 2.4ghz is killing me. like Ichiban said some of my devices uses 2.4ghz like my gps and dishwasher(yes you 'eard me right) and I am this close to switching to linksys EA9500 from my AC88u. Lemme hit that channel 10 and 20hz too and see if it helps.
I've been so frustrated with the 88u. Practically all my devices use 2.4GHz sadly. And it's not just as simple as upgrading the wifi cards in them either!
The only way to get this router stable for me nowadays is to do a reset once in a while.