Yeah I get the same server error (have done for 5 days) when I try to access "My Maps".
First encountered issues when I edited a map and noticed it didn't process the new uploaded saved world. So I tried again and the same thing happened.
I deleted that world map and tried uploading from scratch (i.e not editing a current world).
I started uploading the world archive in step 1, then when it prompted me to attach the PNG file (step 2) it appeared to upload the image successfully but then the thumbnail previews would appear as the "image not found" image. The panel for world details (step 3) then fails to load so I can't progress to the final step.
Hope you can get to the bottom of it