This is a problem that has occurred two times before,

This is a problem that has occurred two times before, and since I have few programming skills, I have no idea how you fixed it. Now all 7 of my sites show a "Page Not Found " error on the login page. The only site that continues to work is the one I have ben working on most recently. The others only have gone through auto-update and have had no other action on my part. Most of them are placeholder sites and are certainly not taxing any programming envelopes that might be causing all this grief. It is giving me second thoughts about my decision to go exclusively with WPMUDEV.
I'd like some help from a staffer as opposed to a helpful user, in that taking that advice in the past has led to even bigger problems. Not to besmirch users with good intentions, but I thought as a pro user I was getting advice from staffers.