Ok, I disabled WMM APSD, see how that goes. The rest was the same or probably not relevant.
I have a similar problem with a Raspberry Pi Zero, but not as frequent. That one disconnects every few days. So maybe I'll fix both of them.
Discussion
Initial run doesn't look too good. Several reconnects/restarts within an hour. Now running for ~90 minutes, so far so good.
I find it strange it's on an irregular interval. If it's power management or something like that, I would expect reconnects on a fixed interval, maybe?
Look at RSSI