Screen Options menu won

Hello WPMUDev'ers!

As you already know, WordPress 4.7 is now out and, I believe this could be related to that upgrade. I have a few websites that I haven't upgraded to 4.7 yet, but all the ones that upgrade, the Screen Options won't come down, and I noticed as well that menus on mobile (backend) do not work either. The icon changes color but nothing opens up.

All these have a theme in common, so I thought it could be a theme issue. Changed to default theme, but still not working. Any ideas how this can be fixed? Thanks in advance.

Best regards,

Paul