Have 32" LG && 27" ViewSonic worked great with Zorin OS 16.3. After geting PC backup and running installed Zorin OS 17.3 and when started only 27" had Zorin with task bar 32"monitor only has Zorin background no task bar. I can drag things from 27" over to 32"
Got it figured out works great now. On start up if I had only the monitor plug in that was to be main monitor and after it had started up plug in the 2nd monitor then it would not of changed.