Musescore files are slow to open on my computer and always start a new window

Say I already have a piece open in musescore, called A. If I want to open piece B, it takes several minutes after clicking on it for it to open. When it does, first a window pops up in musescore asking if I want to restore previous version, after I click yes or no piece B opens in a new musescore window. Why is this happening? Pieces used to open right away in the same musescore window that's already open and I don't know why it's being like this.