I'm almost sure I could solve the problem, but need some more testing to be 100% sure. Here is what I did:
I upgraded XOrg from the repository
(So now I have xorg-x11-7.6-166.1.i586 installed along with all the libraries etc.)
Reinstall the Nvidia driver, because installing a new XOrg touches some files in a way the driver doesn't like.
Since then it seems my issues are gone! Please let me know if this also helps you.
Thanks and kind regards,