I'd like to get Stief's opinion here. But you can in meantime always have both accounts running simultaneously. I often have several accounts running at same time. Since it's easy to swap between accounts at any time.

Have you tried a SAFE Boot & Repair Permissions?

(I must admit my 4.18 refused to run at all (nothing happened when program clicked) & stepped back to 4.16. I need to try again to find what can fix the problem for me, the normal things I'd try didn't have any effect at all. Though I didn't try another account or java settings or a couple other things.)

Honestly I wouldnt care about going back to 4.16 if that means it will run good