Basically, 2.4GHz interface will start acting up if loaded too much. 5GHz is rock solid. For me, it was the same in 18.06, 19.07 and 19.07.1. replacing ath10k-ct with (newest version of) ath10k did not work either.
Currently, only thing that seems to work is to revert to older driver:
Well if that is the case then backdating will certainly fail. But according to gentleman in that thread, backdating to older ath10k fixed the issue with his 2.4 stability?
Different wireless hardware, different driver - ath10k isn't involved with the 2.4 GHz radio at all.
If you had problems with the 5 GHz radio, switching to a different firmware might help, but not for 2.4 GHz.
I am currently using "backdated" ath10k and running same sort of "test" on 2.4GHz...if it keels over (which it should withing 1 day) we will know for sure.
The interaction could be out of memory because the -ct ath10k uses a lot of RAM. There is now -ct-smallbuffers which must be used on devices with 64 MB of RAM and might help on a C7 even though those have 128 MB of RAM.
Either ath10k-ct kernel module can be used with the same ath10k-firmware-ct. The ath10k firmware runs on a CPU core inside the 5 GHz WiFi chip, it has no connection to the main CPU and 2.4 GHz WiFi.
3 days later and 2.4GHz is chugging along quite nicely. It should not work but it works...fitting backdated ath10k firmware fixes 2.4GHz stability. Go figure.
Update: switching ath10k drivers does not fix 2.4 issues Five days later, 2.4 keeled over. Some clients just stopped responding (but were still associated), new clients could connect but not surf. Two hours later, new clients could connect and surf but old (that were already connected) could not.
Any other hints on how to troubleshoot? Can something be done with ath9k drivers?
No, but I tried -ct, non-ct and backdated firmware version. It takes couple of days for issue to manifest itself so it is very cumbersome testing. I am getting somewhat sceptical that you can fix 2.4 radio issue by swapping different 5GHz drivers ... it did not work with three different drivers.
And it is sneaky issue...it appears to work but will start dropping packets or doing some other nasty stuff after couple of days, if subjected to enough load.
At the same time, AR5BXB92 in x86 router running OpenWRT just keeps on chugging with same client load, month after month.