Mi router won't connect to 5G anymore

[Owerdoes]

I use a Mi 4A router as a repeater, connected wirelessly to my providers network.
Last night my router just stopped working, this morning I did a reset on it but it won't connect to my 5G Wi-Fi only to the 2.4G one.
Is it a bug or something new they added?

 

[BartS1975]

I have exactly the same problem today (of course, I also reset the router to factory settings as a test, no change).

Were you able to solve the problem or is it probably a hardware defect?

Edit: I have already found the cause: My main router had automatically set a channel that the Mi router apparently does not support.