@Virgo 

I don't live in a dense neighborhood where interferences from neighbors could be a problem. I have only few visible hotspots and their signal is weak. But I noticed that two of my EAP670 hotspots were configured to use the same channel #1 when channel setting is Auto. I changed channel setting to use #1 on one hotspot and #8 on another and it worked without reboot for whole 8 days. But unfortunately today the problem repeated and I had to reboot both hotspots to restore 2.4 connectivity. It looks like that I need to reboot hotspots at least twice a week to have a reliable service. Is it the level of stability expected from tp-link?

  @Virgo 

This is quite embarrassing that access point with just 3 days uptime is gets disabled 2.4 connectivity and I have to reboot it. You sound like it is normal for tp-link hardware but I want to assure you that this is not normal for any networking equipment that should be able to work 24/7 for months and years. I wish I could return tp-link access points but it is too late by now. Is there any way to contact tp-link to make them aware of this problem? Do I have faulty hardware that could be replaced while it is in warranty?

  @Gregory76  Not sure of your location but here are links to US product warranty information and support. There should also be a chat option on these pages and I found they do respond.

TP-Link Product Support - Wireless Networking Equipment Support

TP-Link Product Support - Replacement and Warranty

If both of the EAP you mentioned are having the same issue, I would doubt faulty hardware, but stranger things have happened.

I have 5 total EAPS, one wired and the rest remote (MESH), 15 Security Cameras and 50 clients (25 wired / 25 wireless / 12 5Ghz and 13 2.4Ghz). I schedule my equipment to reboot once a month so that is virtually the only downtime I have seen after having this system in place for over a year.

How many is "a bunch" of cameras that you mentioned? You stated "since you switched", what were you using before and is there a particular reason you switched?

  @RickJamesBish 

Thank you for the links, I am in US too and I wrote a warranty request. I'll write here what comes out of it.

As of now I set up an omada controller and established reboot schedule to reboot both APs every night. I don't view this as an accptable solution because there is no reason that this hangup always happens after more than 24 hours, also raspberrypi that runs omada controller is not the most reliable system and may fail too.

I have 5 Blink Mini cameras and 2 Blink sync modules that are constantly connected to 2.4G WiFi and 9 Blink XT2 battery powered cameras that connect to 2.4G WiFi from time to time for heartbeat and to transfer video. I also have 4 Leviton smart switches that use 2.4G WiFi. Additionally I have 2 self made arduino gadgets on ESP8266 based NodeMCU dev boards that use 2.4G WiFi. I have a Ecowitt weather station and a GMC-500 dosimeter that also connects using 2.4G WiFi. I have 2 Nest smart thermostats that I think could also use 2.4 WiFi exclusively, not not sure about these. I also have a Roku TV streamer that has only 2.4G connectivity. I have an old asus laptop that has only 2.4G WiFi, maybe there are some more devices in my house that use 2.4G WiFi, e.g. a printer. Clients are divided roughly 50/50 between two access points.

With a list above it should be clear that 2.4G connectivity is important and while it is low traffic a lot of devices use it and cannot use 5G band. I need stable 2.4G WiFi in my house because with time the number of such devices will only increase.

  @RickJamesBish 

I forgot to answer your last question. I used original Arris BGW210 router from AT&T with WiFi extenders and Mikrotik hAP AC (configured as a switch and access point) for 2nd floor. I switched because I wanted to have opnsense router, separate VLANs for IoT devices, I wanted WiFi 6 and I didn't like Arris router instability because Nest thermostats couldn't connect to its WiFi after 2-3 months so I had to reboot it. It was the only wifi incompatibility that I had, all other wifi clients worked just fine and the problem happened quite infrequently. I never ever needed to reboot Mikrotik, it is a role model of a stable networking equipment.

  @Gregory76 I hope you get it sorted. IMO that is a lot of 2.4ghz devices in proximity and I do not envy you sorting this out. You say it worked fine prior to changing out so you would expect it to work in a similar manner. Its possible that if the equipment was set to AUTO, it picked channels and channel widths that worked, and the new equipment did not.

The only other advise I can make is be sure that you separate 2.4ghz channels of each AP. For example if you have 3 APs then manually set to 1, 6, and 11 or 1, 6 and 1 depending on distance between the APs, to have the least amount of overlap. Also try manually setting the channel width. If it defaulted to 40, try manually setting each to 20.