the same with my router TL-WDR4300 2.4GHz band repeated signal failure, but 5GHz band just fine after about 4 or 5 years of use.

I turned on and off Hardware NAT.
I was restoring factory settings.
I downloaded the latest firmware.

Nothing helped, it was enough to copy the data over a 2.4Ghz wifi local network and after some time the router was blowing out the network, i.e. the network as an access point on 2.4Ghz was and could be connected to it but there was no internet or local network, and the message was DNS something

So far, instead of "Auto" I set the channel width to 40Mhz and somehow works. Local speeds reach from 20MB/s to less than 1MB/s until they eventually range within 355KB/s but the network does not crash.

And the internet speed reaches 100/10 Mb/s

Same here with AC1750 Wireless Dual Band Gigabit Router
Model No. Archer C7

At the moment I have changed Channel Width from Auto to 40Mhz and right now it works.

If this is not a permanent solution I will be back with another reply.