Okay, I found additional help for the first problem on this forum. The threads I was hoping to finally appeared when I posted this question. I followed the advice posted by the community and it seems to have worked: Go into Safari > Preferences > Privacy > Details > select "apple.com" and click Remove (thanks to BasementJack and JHdeVilliers). What I do not yet know is whether or not I'll have to repeat this action now. But it's a good start. However, iTunes Match is still a mess - no improvement.