I have had a problem arise several times over the years only with Google Maps in MP and always seems to show up after I try to prefetch a map area. What happens is after a prefetch attempt or I end up starting a prefetch and then canceling it the satellite maps no longer show up and update and result in a 503 error. After spending a lot of time on this and trying to figure out wha happened including un-installing and reinstalling MP I found that if I change the source network that I was using to update the maps everything cleared up. I think what is happening is that Google is blacklisting the address I used when I tried the prefetch. I only noticed this when I cam across a post in another forum.
https://productforums.google.com/forum/#!topic/maps/JICI0tNjPw8
The forum states that this only happens when the Google APIs are not used and the developers only use a URL to fetch the maps. I know that over the years there have been a number of reports of this issue but It only seems that it kind of just goes away. Can anyone else confirm that this might be happening?