@mathijs727 Hello. In my case it was only a matter of time. It takes 5-10 minutes to establish the connection in band 3 although it takes only a minute or less in band 2. Could it be your case?

@TP-Link Hi, again. Sorry. Thought you were asking for the extender model. Router model is ZXHN H298A V1.0 V1.0.25_DIGI.1T12. And could you please help me check one more details: when the router was...

@TP-Link Hi, The test case is correct. Model number: tp-link AC1750 Dual Band, RE450(EU) ver 3.0. Thank you!

@Solarex The same happens with my RE450. When I try to set channels 100 and above the RU extender detects the new channel but cannot connect to the router.

I spend several hours trying to connect to my wireless router wifi 5Ghz and it was impossible until I switch off auto mode and select manually channel 60. With Channel 100 and above it was impossible...