I have upgraded my Redmi AC2100 to OpenWrt 21.02.3 and disabled the scheduled reboot task to see if the issues persist.
I have also bought a Xiaomi AIoT Router AC2350 because living with those issues was frustrating. I will replace the Redmi with this one, and leave the redmi for testing only until it's stable and can be used again.
Additional bit of info:
My Redmi AC2100 is also working 24/7 as a WDS bridge over the 2.4GHz band (I have another router in the storage building of ours connected to the AC2100 as a WDS-client)
Thanks for the feedback, you have a similar setup to mine but I have both bands with the same SSID.
With OpenWrt 21.02.3 the original issue has apparently been fixed, but... I have noticed a new one
After aprox. 24h of uptime the 5ghz band will deliver a maximum of 60mbps. A reboot of the router will allow speeds of symmetrical 300mbps (maxing out my ISP connection) from the same client device at the same distance to the AP.
I made sure that I was connected to the right AP and the right band with wifi analyzer before the tests, I tried to restart the 5ghz interface but that didn't fix the issue, only a reboot does.
I'm happy that at least the original issue seems to be fixed, but I'm still pissed off because I have to keep the daily reboot on the router to prevent this "speed lock" from happening.
A software reboot DOES NOT WORK. Only unplugging the router resets the high performance of the 5ghz band. This is the weirdest issues I have ever seen.
After unplugging and plugging the router power brick, I can get 300mbps on 5ghz.
Both issues are still ongoing, the 50-60mbps "limit" on 5ghz after a few hours of uptime and the random "no internet" issue on both the 2.4 and 5ghz bands...
I do not understand how can I be the only one experiencing those issues. It's not about the dumb ap config, I have a xiaomi router 4a gigabit with the exact same config and openwrt version running flawlessly and has always been like that.
I took a look at your config in the first post and I am seeing a couple of differences that you could try changing. For one, I like to set cell_density to 2 -- I am almost certain that this will not change your situation one whit, but hey, can't really lose much from trying. Secondly, I had to set option reassociation_deadline '20000' for the wifi-ifaces after I enabled 802.11r; without that, I had random disconnects or other weird issues with some devices.
I have changed cell density to 2 (High) and reassociation_deadline to 20000 in both the 2.4ghz and the 5ghz band as the disconnects happened on both frequencies.
I will disable the daily reboot, and I'm hoping to see if this fixes the issue. Thanks!
This seems to have helped, I apparently no longer have wifi disconnects. Thank you!
I still have the issue that after 24-48h of uptime the router limits the 5ghz band to 50mbps, I will rollback from 21.02.3 to 21.02.2 where the issue was not happening. I will report back and see if this solves both issues.
Finally after changing cell density to 2 (High) and reassociation_deadline to 20000 in both the 2.4ghz and the 5ghz band, and a downgrade to OpenWrt 21.02.2 both issues have been solved! Thanks everyone