My client had a similar issue, most sites worked but DMV and a few others wouldn't load. I messed with it for a while but what ended up working was cloning the mac address of the PC connected to the router. After that everything worked. Give it a shot!
Upgraded an AC86u from 384.13 to 384.15 via teamviwer and the router never turned back on.
I'll probably be on-site tomorrow morning to fix it, anything I should report back to prevent issues for others?
I've advised the site to turn off the router and unplug a usb drive with jffs scripts like...
When you do the restore utility or try to load the Mini-CFE webpage you should have set a static IP for your PC. After setting a static IP you can interface with your router while it is in recovery mode.