Help with login issues

Hi, guys, I hope you can help me shed some light on the following issue:

After installing Multi Monitor Wallpaper, my Hackintosh's login was completely messed up. Even after uninstalling it using appzapper. First, monitors 2 and 3 were changed, but that isn't an issue by itself. The main issue is that apps don't keep their display "assignments" - say Word on display 2 or Safari on display 1 - or even worse: their show up at 2 when assigned to 3, randomly. Even if I re-assign the correct display, it seems the option isn't save for the next login. Same happened with an app that I took out of my "open at login" app list and it kept opening, as if the change were never made. Finally, my wallpaper selections are all messed up - sometimes they show up, sometimes they don't and default to the usual Mac one.

Needless to say, before installing that app login worked perfectly.

My config is: Intel Core i5-7400 3 Ghz ASRock z270 Killer SLI/BR Radeon RX580

I'm using the MacPro6,1 model to make my three display set work (two displayport, one hdmi).

Any leads?