Got the well known issue with the nvidia driver on a ASUS GL552v. Current issue: After changing back to 16.04 on Kernel 4.15.0-30 found the square around mouse pointer as also mentioned in question 947375. Managed to temporary solve it by using sudo systemctl restart sddm But I would prefer a permanent fix and already tried the suggestion of re-installing x-org files. Unfortunately no success in fixing problem. Any ideas for a permanent fix?
For those who want to know - How I got to this point: Had an earlier version of 16.04 working fine for over 1.5 years after overcoming initial installation problems by removing second hdd and using the 'nomodeset' command. Then, after successfully installing 18.04 on 3 laptops I've decided its now time for my own to get a clean install and upgrade to 18.04. Only to discover the lagging problem in regards to problems with nvidia driver. After many hours of not finding any solution decided to go back to 16.04