Google Maps Guide, Cecelia, created a Google Maps Help thread warning users not to edit their Google My Maps. The specific issue is with editing the Place Details in the My Maps. If you do edit it now, it may impact the rest of your information on your map.
We are aware of a temporary technical issue with My Maps. Our teams are working hard to resolve this issue. Until everything is running smoothly again, we recommend that you do not edit the Place Details of locations on your My Maps. This may impact the rest of the information on your map.
Thank you for understanding. We'll be sure to update this thread with more information as soon as we have it.
So be warned and hold off until you hear an update from Cecelia in the Google Maps Help thread.
Forum discussion at Google Maps Help.