I've compiled a build with NSS version 11.4 and Ath11k FW 2.12 (still this is the bloated build with lots of unnecessary NSS modules) and flashed it to my QNAP keeping the settings.
It looks like the Inactive time isn't OK.
'iw' 'dev' 'phy0-ap0' 'station' 'dump' | 'grep' 'inactive'
inactive time: 566360 ms
inactive time: 5680430 ms
inactive time: 2324200 ms
Before that I had a build with older Ath11k 2.9 FW and NSS 12.5 and it looked to me that Inactive time was reset from time to time.
Probably I will have to start with just the basic NSS .config file.
Edit - I've just tried a build with NSS version 12.2 and Ath11k FW 2.12 (still this is the bloated build with lots of unnecessary NSS modules) and flashed it to my QNAP keeping the settings.
With this combination Inactive Time really seems OK. I still have a 80 MHz cap on RX chain though. I will test it for some more days.
Currently I cannot test mesh nor WDS.
These inconsistencies are really irritating but your efforts are simply amazing.
Thanks guys!