To add to @Rich2005 post, an over sized brush will also look like this behavior.
A simple Ctrl+C and the clipboard selected you got your "brush" at 1024px, you got an over sized brush thus that cross without the "brush" shape visible (because you're zoomed in) and not working as expected.
a 50 second video with 2 examples > https://imgur.com/Sls6fRe
A simple Ctrl+C and the clipboard selected you got your "brush" at 1024px, you got an over sized brush thus that cross without the "brush" shape visible (because you're zoomed in) and not working as expected.
a 50 second video with 2 examples > https://imgur.com/Sls6fRe