Only connects to 2.4 wifi

I have RT-AC88U.. rebooted router and phone.. it seems to be stable for the last 15mins.. Let's see.
 
I have the Asus RT-AC3100 and the mobile app prompts me to switch to 5 GHz for better speed and it does, but it stills show the N7 on 2.4 GHz. Idk...
I have the same router and have no problems seeing both 2.4 and 5 ghz networks.
 
I have the same router and have no problems seeing both 2.4 and 5 ghz networks.

I see the 2 networks but it switches back sometimes. All day today is has remained on 5 Ghz so hopefully it will stay that way.
 
I gave up again, after a day use it kept disconnecting often, so remove the WiFi Mac filters to let it pick what mode it wants, somehow it always just likes 2.4