I have observed the same (wifi drop and reconnects in seconds, noticed during video call) while using Merlin's firmwares 384.13 - 384.19 on my AC86U. It happens regardless I turned Airtime Fairness, MIMO, and Beam-forming ON or OFF.
I have seen multiple discussions and suggestions, and. have tried some of them:
- Turn off Airtime Fairness, MIMO, and Beam-forming (not work for me)
- Use non-DFS channels (not work for me)
- Use Merlin 384.12 (haven't tried yet)
- Beacon Interval from 100 to 50 (from a Chinese forum and many replies said this solved their problem, but I haven't tried yet)
- Switch from Merlin to Official (currently on this, 3.0.0.4.386_40451 seems working for me)