For me - first I couldn't use the change option on resort reservations, then I couldn't see or book annual pass holder rates even though my account was correctly showing a valid AP, then I couldn't see any magic bands or cards at all.
Final straw(s), November 2017 front desk CM's could not manage to code any of our MB's to work on the doors for more than a day or two. Per advice from Guest Relations (after an email from me explaining my issue) we deactivated all but one or two MB's and still had issues on our Christmas/New Years 2017-18 trip. Again contacted GR prior to our Easter trip and were told all was well we were fine! I had read the thread about others making new accounts but my contact at guest services didn't recommend that for me at the time.
I was worried about a family reunion trip over Easter and my fears were valid unfortunately. Despite having only 1 MB for 5 of a party of 7 (some had 2 or 3) we were consistently having problems accessing our rooms. We made 9 trips to the front desk for an 8 night trip, no exaggeration and it was random as to whos band would work/not work on any given day! The worst was when my mother in law (celebrating her 85th birthday) walked back to the room for a rest after being at the pool and couldn't open the door. Luckily my niece ran back shortly after for something and let "nana" in - ugh.
So after sending another email with our Easter trip issues; as of today, I am now the proud owner of a 2nd MDE account

I did have to set up a new email and a new MDE account, after that guest services and IT did the rest.
All of my information was transferred without issue including future resort reservations, fast passes and photo pass, so far so good.
If your not having issues I would leave well enough alone but if you start having problems using MDE then the process is easier than I anticipated.
Sorry So Long