@WreckRox 

When you run Network Optimization, two things happen: Deco mesh forces devices to briefly disconnect and reconnect, and Deco may also switch WiFi channel, but not necessarily.

Have you verified that Network Optimization does change 2.4GHz channel when you run it? Have you considered that maybe you are getting service back on those devices just because they were forced to reconnect? Next time they lose Internet, restart these phones and do not run Network Optimization. See if just phone restart makes it connect to Internet again. If it does, what you have is a phone problem.

As far as I know, TP-Link development rejected manual channel setup. They promised Deco reboot on schedule, which does the same as Network Optimization, because after reboot Main Deco will rescan WiFi networks and choose least congested channel (at least, in theory). ETA for scheduled reboot is unknown.

You can emulate that with little expense. Connect Main Deco to power through smart plug, set schedule on smart plug to power off/on Main Deco every X hours.

@Alexandre. yep I have confirmed that it does change the 2.4ghz channel every time network optimization is run. The wifi above my apartment has a router that turns on periodically and more often than not is the cause of the interference.  I can't change that so I need to do something from my end.

About the reconnecting thingy, it doesn't change when I reconnect the devices near the affected deco. They start working whenever the devices are outside the "zone of influence" of the interfering wifi. Our apartment has two decos and the wifi which interferes with our network is in one half of the apartment. So, the main deco is unaffected and one of the satellite deco's 2.4ghz stops working.

@WreckRox 

At  a time, I plug the deco units to a smart plug and put it in an on/off schedule for it to reset.

Once the decos reset, it should re-optimize.

@Raph062384 Unfortunately, it's not an option for me. The decos take a lot of time to boot anyway. A minute is a lot.