EX6100 terrible wifi speeds on Windows 10 - R7000 router works fine

I recently update to Windows 10 on my Dell Studio laptop 1735 (with Dell Wireless minicard 1510).

When working via my Nighthawk R7000 everything goes fine.

But when I connect to my EX6100 2.4 or 5 Ghz channel speed drops to 1 mbps...

I also have a Windows 10 tablet which works just fine with the extender, as does IoS devices.

I already tried to update the Network adaptor drivers via device manager but, unless I choose the one mentioning "Microsoft", I get a blue screen...

The EX6100 also has the latest firmeware

Any ideas which settings I should change on my laptop?

Thanks!