RBR750 - unstable, satellites keep disconnecting

Hi all,

Starting to lose my mind on this.

RBR750 + 3 RBS750 satellites running in AP mode. I have a separate DSL router which acts as DHCP; the Orbi is purely wifi. We've got a fairly busy household - probably 40 ish devices.

Have had it for several years and it has mostly been solid.

About a week ago started getting issues with video calls (really poor quality / laggy) and after a quick look realised that the computer had connected to the router directly (far away, rather than the satellite which is nearby.)

Didn't think much of it short of cycling the power on the satellite.

Then next day, all wifi was down. Even connecting over Ethernet would refuse to do anything. Power cycled everything and that brought it back. Noticed that it was on the 4.* version of the firmware and managed to update it to 7.*.31.

Next day, wifi is mostly down - the RBR seemed to still be fine but the Orbi Admin panel was showing all three satellites as disconnected. Power cycled everything.

Then it happened again. This time I powered off all the Orbi, and left for a few minutes, then powered up the RBR, waited for it to be online; then powered up each RBS (starting with the one closest to the RBR and going to the furthest one, which often backhauls via one of the RBS) but each time waiting until it was online before moving to the next. Again this worked for a while, but only survived a day before all satellites are disconnected again.

Next I performed a factory reset on the Router (using Admin > Erase, etc.) and all the satellites (using the paper clip hole.) Restored a backup of the config and got everything going again.

(Sidenote: one strange thing about this factory reset. I wanted the RBR to run through its setup process after reset, and that included searching and finding the RBS. So I brought them all in to the same room as the RBR. However, the RBR would not find any of them if they were all turned on at the same time. If I just turned on one RBS then the RBR would find it almost immediately, so clearly some strange interference happening.)

(Sidenote 2: I have often wondered if I am slightly overprovisioned with the RBS and whether decreasing the transmit power on them might be a good idea.)

This survived about a day and a half before again everything disconnected, including the RBR, can only get back on wifi by power cycling everything. That was about an hour ago and in the time it's taken me to write this, wifi has gone again and I am now on hotspot.

It's unpredictable as to when it will all disconnect. What options do I have? Should I consider downgrading to a different v7 (possibly .21) firmware? Or maybe back to v4?

Thanks for any help.