Steps to reproduce the issue

Start a new module - in this case a Custom module.
Resize browser screen from full size (on desktop) to about half screen width
Click the Position drop-down arrow

Expected result

To see a list of template positions

Actual result

Drop-down menu shows only two items:
"Type or select some...
No results match"

See screenshot:

System information (as much as possible)

Happens on both Firefox and Chrome
On CloudAccess.net joomla.com website

Additional comments