R7800 Google service issues

I recently updated my R7800 firmware to 1.0.2.44 and yesterday noticed issues with Google's services.

1) On my Oneplus 3 I could no longer dowload updates from Play Store on wifi. Updates downloaded correctly over 4G connection.

2) Youtube would not load videos via web page or app on iPad 2017. Youtube videos load very slowly on Oneplus 3 and Windows connected via ethernet cable. Youtube works without any delay over 4G on the phone and over tethered 4G on the iPad.

I tried reseting stuff on the devices, rebooting the router and restoring factory settings but nothing helped. I finally installed Voxel's firmware 1.0.2.46SF which fixed the Play store downloads but Youtube videos are still incredibly slow to load on the Android phone and don't play at all on the iPad. I guess the slow Youtube could be related to the ISP, but I get steady 99/10 on speedtest so the router seems more likely. Also since the 4G connection loads the videos much faster, it seems it's not a Google issue either.

Any ideas?

Edit:

I tried disabling WMM and detaching my USB hard drive from the router, no effect.

Edit 2:

Actually, the slow Youtube does seem like an ISP issue, confirmed by connecting my PC directly to wall plug bypassing the router and Youtube is still slow.

P.S

I wanted to notify Netgear of the problem with the firmware but there's no email address for customer support, just options to use the community or paid support. That's pretty weird, gives me a real dodgy feeling about the whole company.

Not to mention, when registering a community account it allowed me to setup a 32 character password no problem, but when trying to log in gave me an error on the length, forcing me to user the password recovery and change to a shorter one.