I have the same issue.
My current work around:
- Go to window->viewports and open a second viewport tab.
- Click the upper left corner of viewport 1 !
- Now close viewport 1.
- Reopen viewport 1 from window->viewports menu.
This at least works for me. Hope it helps until the bug is resolved.
-F4Q
UPDATE:
Just figured out that my answer is obsolete. The easy way is to simply hit shift-d in the selected viewport.
- Shift-d for default viewport.
- Shift-c for cinematic viewport.