Potential duplicate of 5 GHZ network gone
I can also confirm that Wifi is flaky on Omnia, with 5.1.2 (was rock stable on 3.11) - could very well be the firmware IMO, I’ve seen that at least on stock OpenWRT new qca9880 firmware updates are rather common as of late (there’s a couple packages I like to have bleeding edge, mainly haproxy, so I do regular builds, and every once in a while cleanup my dl/ folder manually, that’s how I noticed).
Resetting the router generally works for me, but the next time my Wifi fail, I’ll try to grab some specifics.
To be fair, I’ve had to replace the Zenner diode and the electrolytic cap (after managing to plug my 27V speaker supply in the Omnia :D) at roughly the same time I did the 5.1 upgrade. But still, given that the thing works just fine even without those 2 components, I find it rather unlikely that it’s an electric phenomenon.