This issue is two-fold.
1/ the length of your forum category title.
There really isnt a problem in the length per se, so much as the incorrect "nowrap" class added to that element within the breadcrumb bar. This has been corrected for UBB.threads 7.7.2. Until that version is posted, you can easily resolve it by moving your Forum Description out of the Forum Title, and putting it in to the Forum Description section. OR if you feel comfortable modifying your forum code, you can perform a simple patch/edit that will resolve the issue until v7.7.2 is available with a proper fix:
FIND: (there are 3 of these)
$breadcrumb .= " <span class=\"nw\">
2/ the second issue is the old/classic "Jump Box" menu in your forum footer.
This is also affected by the length of your Forum Titles. And this again isnt directly a fault of yours.
Enable the modern HOP-TO menu.
Go to: Control Panel > General > General Display Settings
Towards the bottom of that section: "Hop To" Popup Menu Width
This will disable the classic "Jump Box" in footer, and enable the modern "Hop-To" menu in forum/topic navigation menu, and will truncate (with ellipses) the forum titles to 50 characters. The classic "Jump Box" hasnt been updated to support mobile layout. It has been overlooked since 7.6.0 was first released. But now that you've put attention to it, you can expect a proper update to happen there.
Thank you for reporting this!
EDIT: both of these issues are now fixed for UBB.threads 7.7.2
Again, thanks for reporting this!