Had 2g/5g wifi issues on 5+ apple devices; facebook app worked, safari didn't, nor did the app store; wifi laptop connected just fine with no issues. Same results with both RT-AC68U_384.6_alpha revisions g4284a1146 & gc644a0c; reverting back to 384.5 worked just fine. Apples worked with 385.6 with factory defaults; but importing settings & jffs backups resulted in the problem reoccurring. 384.5 fixed the problem swiftly without having to mess around. I'm assuming manually changing the settings without importing a backup could be a work around, have you found this often to be the case also?
Wifi is outside of my control, and is often more influenced by configuration/environment than by the driver itself. Disable airtime fairness and implicit/universal beamforming for starter, quite a few devices have compatibility issues with these.