My only problem is to believe its a hardware problem
Having struggled with four different AC86s there are several things that lead me to believe it is a hardware related issue and specifically something about the memory:
1. I have had AC86s where restoring to factory defaults and checking the box to clear all settings in the GUI has resulted in the router appearing to go through the process but when it reboots all the settings, password, SSIDs, etc are unchanged. Then the only option was to do a NVRAM erase followed by a factory reset.
2. I have had AC86s where even after doing multiple "Nuclear Resets" the firewall rules installed using Skynet still seem to be functioning and blocking IPs and IP ranges for countries that I had previously added to the default setting. This is after the resets and before I have reinstalled any scripts. I can see the blocks in the Log and AIprotection shows no hits over several days which is unusual if Skynet isn't running.
3. I have had an AC86 make a mishmash out of the 20 Static IPs I have entered. I have also had an AC86 just drop/ forget the list of static IPs.
4. One of the AC86s was in such bad shape that you couldn't load firmware in the recovery mode. It would go through the process, say it was completed but the firmware version was the same as before and none of the settings were set back to default.
5. VPN clients don't continue to function as the DHCP server for the VPN tunnel fails/resets to 0.0.0.0. Only fix is a "Nuclear Reset".
6. Multiple times with several of the routers where I could not log into the router using the GUI. The easiest solution was to SSH in and command a reboot.
7. Finally since the majority of users have no problems with this router it seems unlikely that either ASUS or Merlin's firmware is the issue since then most everyone would be having problems. I run the same settings on my AC1900P I had to buy while my AC86 is out for repairs since June and I don't have any issues so it probably isn't my setup or Merlin's 384.13. I have had issues with the AC86 going back to 384.9 so nothing has changed in Merlin's firmware causing the problems.
Your supposition about the radios may be correct. It is strange that this is an issue with no solution. Based on the posts on this forum or the negative reviews on Amazon gigging the 2.4 Ghz radio and the issue of it locking on channel 0 it isn't uncommon. It is just unfortunate that there isn't a method to put the router into a stable state and keep the radios functioning.