EAX12 AX1600 drops connection constantly

I have an Orbi #RBR350 that doesn't quite manage to make it to the final room of the house. I bought an EAX12 AX1600 to use as an extender to reach the final room. It drops after 30 seconds, throws a tantrum, and devices revert back to the Orbi. Both 2.4g and 5g drop continuously after 30 seconds or so.

The EAX12 wifi channels disappear for a short time, before coming back to life. They'll drop again shortly after, and the cycle continues.

What I've tried so far:

• All firmware is up-to-date.
• 6 reinstalls.
• Power-cycling.
• All Netgear chat support options have been trialed, including changing the Orbi router to optimal settings (DNS & wifi channels).
• I have tried 6 different placements and locations, between 1 and 9 meters apart, even straight lines with no barriers.
• I have installed through Nighthawk and through directly logging into the device itself.
• I've tried using one SSID, and keeping them as separate _EXT channels.
• I had an older Netgear extender that worked, but it was really, really slow - this was meant to be an upgrade.
• Multiple speed tests - they're all excellent.
• The lights are almost always all green, the router one does occasionally go red, or turn off - but comes back green shortly after.

Is there a solve for this or are these products just garbage?