Filters and sorting DDLs not working after upgrade on default "Forum - Thread List" widget (Case #1627)

For some reason we can’t open “Filter” or “Sort” DDLs on "Forum - Thread List" widget after upgrade to from 10.1.0 to 10.1.5.9189 on our both DEV and QA machines.
Nothing happens when you click on DDLs, w/o any error in DEV console or Community log.

They are still working in Production (v.10.1.0):

We are using default built-in version of the widget and site theme w/o any customization.

We went through “User Experience Upgrade” process during the upgrades in both environments, approved and committed all changes to theme, pages and widgets.

Also I found that on environments we’re missing following jQuery functions:

Production:

DEV/QA:

We checked that we have this script present in the widget and there are no errors in the Chrome dev console:

Our developers found that the problem could be in screen.less file. When we disabled height for  .uiselect.options > div > div  and position for .uiselect  it looks better but not perfect:

Anybody had a similar issue or has an idea how this could be fixed?

We opened support case #1627, but no luck yet.

Thanks, Vitaliy.