MuseScore 3.0 Scoring System

I use MuseScore to compose and arrange scores (ranging from string quartet to symphony orchestra) and there seems to be a problem with the key signatures and clefs in the 3.0 version. They show up in very unnecessary areas, about every four measures, and it's quite hard to read a part with so much mess on the page. I have to go through a delete all of them, but sometimes it either won't delete or it gets rid of the key signature and there flats and sharps to deal with instead. I did change the courtesy setting, too, but it didn't do anything. There's an example below. And when playing back individual parts, how do you listen to just one part at a time? I love being able to hear other parts when I'm playing along with my instrument, but I'm not sure how to mute the other parts when I'm editing only one part of the score.

P.S. I was told to recreate the problem. I'm not really sure how the problem happened. Once I downloaded the MuseScore 3.0, and the program had to reboot my old scores from 2.3.2, I began experiencing that issue. It is even worse when I create pages for each part (go to File, select Parts... and click New All. Then you'll be able to look at individual parts instead of the whole score). I don't know if I'm the only one experiencing that issue. If so, it might just be my computer freaking out on me.