I only have my UM1 for a few weeks now, but not enough time to play with it due to exams. One of the prints I had this on was without overhang, I believe it was this SketchUp file I converted:
https://3dwarehouse.sketchup.com/model.html?id=8f187dc09654501c70f2373efbf66671
The top of the dome showed the same effect, but because it was not an overhang, it was only forming a curly turd like top. Will post pictures as soon as exams are done.
But I believed it was due to the small surface area and the constant heating of the nozzle. Even though it might have been the minimal 5 seconds, I believe that the proximity of the nozzle is enough to mess with the temperature.
I think I saw a Z retraction option somewhere in expert settings, making the build plate lower when waiting for the next layer. Perhaps that is something you can test?