Cannot Select & Assign User via Test Player

When populating a Test Cycle with Test Cases, I am attempting to select an assignee but usually my own name would be suggested.

Typing in a few letters for a name and the search just loops

Via the Test Player, this is the same issue

If I then start typing in the few few letters of a name, 'Loading' displays...

But then the entire browser window refreshes.

Is anyone else experiencing this issue?