Problems with clone and brush tools with Photoshop Elements on Mac

Hello!

Six months ago I bought a Mac desk-top computer, and since then have had persistent problems in using Photoshop Elements 14 editor on it. For several years previously I used different updates of Elements on Windows, and had no difficulties at all.

The main problem I have now on the Mac is with the brush and clone tools, which after a while begin to 'stick'  -  i.e. they don't respond to clicks on the mouse, and then leave streaks across the image when they unstick. The screen also flashes unnervingly (only for a fraction of a second, but it's really irritating) when I move the curser from the photo to the tools palette. In any one editing session, this problem occurs intermittently - although the issues persist just about every time I go into the editor.

When I bought the computer it came with El Capitan, but I have now upgraded to Sierra. I am now also trialling Elements 15, but the problem is just the same. I have uninstalled Elements and then re-installed. I have done a factory reset of the computer, (before the introduction of Sierra). I have spent hours with technicians on the Adobe chat-line, with no progress whatsoever. Nothing has helped.

Is there any miracle worker out there who can advise a solution? Thanks!!