@Hawk86eye 

Downgrade to v1.5.5 (it's without openmesh support):

1.5.5 Build 210219 Rel.35914n(4555)
https://static.tp-link.com/beta/2021/202103/20210329/c80v1-up-noboot_2021-02-19_10.17.18.zip

@Kevin_Z Hello, I'll try to make a video when it will occur again.

But now I'll try to explain what happens.

Lets say I have main SSID network name MyWIFI123 for example. Everything works as a charm.... Then suddenly all my devices don't see my SSID and that is, because the SSID changes from MyWIFI123 to ZyXELI123 all by itself and broadcast this name as my main SSID.

I thought that my SSID disappears, but I tried to scan all networks around and by MAC address i found that SSID won't disappear but it changes first five letters of SSID to ZyXEL.
This happens to both 2,4G and 5G or sometimes just to 5G only randomly.

If i restart router SSID is back to "MyWIFI123" and works again for some time - even without me changing anything.
If this happens and I connect to router settings I can see that SSID is set to MyWIFI123 and everything seems ok. So I can disable and enable wifi (just that, no name changing or anything else) and scan the networks around I can see that my wifi name is correct and back again.

And no there is no way anyone in family si able to change SSID as "joke" because I'm the only one who knows the password (strong one) and my kids can't even write yet :)

My guess is that OneMesh is somehow thinking that some ZyXEL device around me is part of that Mesh or is coliding with some device of someone elses wifi.

I'll try to make some screenshots or video if that happens again, because I have never saw anything like this.

Right after I sent the reply it happend again.

So i made a video of it. Me clicking wierdly in the middle is me disabling and enabling wifi in settings.

Around 1:05 you can see how it changes SSID back to original.

@Kevin_Z Thank you. I'll try to make as much evidence of this as possible. I made a few screenshots with SSIDs visible and I'll try to be helpfull as possible.

@Kevin_Z I have the same problem. My 2.4Ghz SSID changes to the 5Ghz SSID + the remaining letters since the 5Ghz one is shorter.

Example: 

2.4Ghz SSID                            : 12345

5Ghz SSID                               : abc

2.4Ghz SSID after the change : abc45

This only started happening today, 2 weeks after the upgrade to Firmware Version: 1.5.7 Build 210308 Rel.60033n(4555). I downgraded to 1.5.3 Build 210128 Rel.64503n(4555) now.

REMINDER TO BACKUP CONFIGURATION if you're not logged in with you tp-link account if you want to do the same thing, since manual firmware install erases config.

@ady1769 Hello Andy, I found that this problem is based on the last WiFi you were connected on with your phone. So for example if you connect to wifi at your freinds house, then power off your display, come back home and turn display on your C80 will get your friends wifi name as its own. I don't know why, in lab they couldn't simulate this issue, but they provided me with beta firmware which looks like it is working, but they never released newer version of the stable firmware since the one with mesh function.

Well never mind. Even beta firmware didn't solve this problem. I just tested it and it changed my SSID again.
So the problem looks like this:
I go somewhere elese, where I connect to their WiFi network. I come back home, try to connect to my network, but my network changes SSID to the name of the previous network I was connected before and I can't connect to my network. The only solution is to reset the router.

I don't know how or why this happens, but in phone is none app to admin the router or something like this.