After about 4,5 years of continuous running of my mesh router(s) the 2.4 Ghz suddenly became unavailable on Saturday.
 

First I noticed it by lights in the house, the robot vacuum cleaner, security devices etc. didn't´t work as expected.

Then when I tested connecting directly to the 2.4 Ghz it shows "Connection failed or Can´t connect to this network" (depending on which device I´m trying from).

I have tested with an iPhone, Android phone, iPad and laptop - all getting the same message.

I then tried rebooting all three mesh devices, no luck. (I also checked that all three devices were updated with the latest firmware, or at least that is what the app is saying).

After that, I did a reset of all devices and did a brand new setup of the whole mesh network - no problem setting it up, but still with the same result.

The 5 Ghz and the Guest network works just fine, it is only the 2.4 GHz that is not working.

I can in the forum see others that are experiencing about the same things as I do, but on different models.

What more can I do, what can cause this issue?