RAX 120 problem communicating with Samsung 5g phone

[gfs10]

I have a RAX120  running wpa2. the router communicates with all my devices, (even though i have found the range is really bad.) except one. if i connect my phone to the 5ghz. it connects but apps do no want to launch and the web browser comunication is hit and miss. if i connect to the 5ghz guest i have no problem and the speed is much better

i have turned off the wifi 6 capability as that was causing other problems 

anyone have any ideas

[Newfiedrool]

As you have 2 posts and seem to have an issue with both AX, WiFi range and devices I wire up a pc or Mac and download the latest update from the support page.

Do a manual update over the top, then reset using the rear pin hole method.

Set the router up as new, do not use a saved config profile. 
Test.