I have similar problem, however it looks it's loosing all connected clients after while and none connect again. I start loosing connected clients 1 or 2 months ago. I'm restarting my AP every day at 3AM and yet it's not sufficient.
Basically, ath9k firmware blobs are buggy and will make 2.4GHz go down after a while. Usually, this will happen when there are many clients connected and lot's of data being transferred. There was a hearsay that backdating ath10 (5GHz) drivers might help with 2.4GHz stability but that has been debunked since. I tried it personally.
People have made scripts that tail the log and reboot 2.4G when it gets stuck but currently there is no definite answer on how to fix it permanently.
I see this is already being discussed elsewhere, yet just sharing, replacing drivers from 2017 didn't help. I will try with small buffers for 5G, if this anyhow improves the situation with 2.4, as already proposed here.
I'm currently on custom build fw, using this configuration - https://pastebin.com/ZdE75rFP - and so far it is behaving slightly differently - while previously I got 2.4 simply lost all connected stations (and none reconnected, as I have another AP in my house), now it seems it hold longer but still after eg. 5-10 hours I have to reboot (even just bringing wifi up/down don't help). I see some devices are still getting connected but not the same amount as after fresh reboot (eg. 3 instead of 10). And those 3 even being connected, there is almost no traffic anyway passed.
Also now I'm using 20MHz instead of 40Mhz, to see if this improves or not as I have now 8 hours uptime without issue.
It would be great, if someone may ask us which kind of debugging info to provide when this happens. @nbd Felix, maybe ?
It seems that using the build I posted config above (developers build), drivers ath10k-firmware-qca988x-ct-htt and kernel optimized driver kmod-ath10k-ct-smallbuffers, in combination with 20 MHz bandwidth, is working solution for me - all 2.4 GHz connections are so far stable.
I had pretty much the same issue some weeks ago when I disconnected my router and moved it. It behaved the same with loss of several ping packages in a row and then 4-5 that went through.
After upgrade, and a total re-flash the issue was the same.
But I also have a router that was provided by my ISP that are connected between the internet port to the outside world and my OpenWRT router. The ISP router had the same ip adress 192.168.1.1 that my OpenWRT router had. I changed ISP router to 192.168.0.1 instead and kept the 192.168.1.1 on my OpenWRT router and it now works. Even if you don't have a extra router on the line there might be a IP collision that results in the same result. Hope this helps
The weird thing here is that I think they both had the same IP address before I disconnected them and it still worked somehow.
My tests indicated that fiddling/swapping out 5GHz drivers to fix 2.4GHz issues is pointless.
ath10 = 5GHz
ath9 = 2.4GHz
You can swap out ath10k as much as you want, it is ath9 firmware blob that has issues and it is proprietary/out of OpenWRT. Mine failed sooner or later. Only way to make it work 100% is to force it to 56Mbit/sec which is not really useful.
I just disabled 2.4GHz and use 5GHz only. It is rock solid and has plenty of bandwidth. 2.4GHz is legacy anyway and not recommended any more.
The theory is that some ath10k configurations may have used too much memory? Also it's not impossible that software conflict happens... OTOH there doesn't seem to be solid evidence that it's definitely the case either.
2.4GHz maybe legacy in the sense that WPA2 is also legacy, it's going to be used for quite some time for quite a few people, especially for low-end devices which don't have 5GHz radio at all.
Sadly, while it's frustrating for those who're affected, it seems unlikely to be thoroughly fixed for everyone considering the complexities involved as there can be many different setups... Am lucky that it's been working fine for me, at least in the past month or so... But for others, I don't know what can be done... Getting a new router? Maybe in a year or two? As 11ac Wave-2 boxes don't seem to be a "big enough" of an upgrade and 11ax support is still in infancy.
I can attest to loyukfai's experience - my Archer C7 seems to be going ok. I use my Archer C7 V2 as an AP only but I've had to play with different configurations to get it to work. Recently, I just switched to the kmod-ath10k and ath10k-firmware-qca988x. I also set a cron job to reboot every morning at 4:30am. It seems to be working really good for me now.
2.4GHz works if you have low bandwidth Internet, few devices and reboot it every night. But it falls apart if you start streaming stuff or have many devices attached to it.
The theory of ath10k using too much memory is not really plausible. My routers are configured as dumb AP's and worked just fine on 5GHz with 50% of memory free when 2.4GHz locked up. LUCI was accesible and you could Telnet to it, it just starts dropping packets or not allowing new clients to associate on 2.4GHz.
The issue seems to be in the firmware of ath9 device itself.