D7800 - PC keeps dropping 5G, but no other device does

[FarleyUK]

I'm using a new Nighthawk D7800 router, and all devices connect to it without an issue - apart from my PC. It's never had an issue before, and it connects to 2.4g fine, but when trying to connect to the 5G signal, I get a constant 'No Internet' message in the WiFi control panel.

Using an ASUS PCE-AE88 WiFi adapter. As mentioned, had no issues before the D7800, including the standard Vodafone router.

Can anyone advise what might be the issue?

[duckware]

This is a huge long shot (if my problem is also your problem) -- but....

I have a R7800 and connect my laptop to it all the time 5G and all of a sudden ran into problems (it was stay connected, but throughput was <1Mbps).  Turn out, this happened when I unplugged my laptop from the power supply (ran on battery).  And then found out that when running on battery, I could fix the problem by running the Dell 'high performance' power plan.  I swear I never had this problem before with 5G on battery.  And I know the R7800 firmware was not updated.  Which might point to a Windows security update as the problem?