Sudden change of active window (strange behaviour on iMac)

ejb1973 wrote:

While working in one application (e.g. Word, Excel, Mail) every now and then the computer seems to activate something else outside of the active window.

E.g when working in Excel, scrolling down or typing in a cell, suddenly nothing happens and I have to actively go back to the screen to continue my actions.

Sometimes I believe it has to do with my mouse triggering unexpected actions, or rather that someone is connected to my Mac as well and purposely uses a shortcut or mouse action to annoy me. Similar to a TV where someone with a secondary remote is switching channels while you are watching your favorite movie ;-)

I have changed difference mouse settings several times, but above behaviour continues.

To trouble shoot further you can:

Try a SafeBoot https://support.apple.com/en-us/HT201262

Takes noticeable longer to get to the login screen, does a 5-15 minute disk repair before it fully boots up, and certain system caches get cleared and rebuilt, including dynamic loader cache, etc. Login and test. Reboot and test will take a little longer as caches get rebuilt.

This test will tell you if third party interference; extensions etc are not loaded in safe boot mode.

Test issue in another user (or guest user) account  https://support.apple.com/en-us/HT204443

This will tell you if it a universal issue or isolated to your user/admin account.