We have just completed the update.The bug seems to be fixed!However, after the maintenance update we had the following error message:"Health Monitor is running, with an error. ( [Role] Primary [State] HA not Configured ) initHealthMonitor(): can not ...

 The release notes for version 3.10.4 contain the fixed bug CSCwe22074...that sounds very much like this problem

Maybe - an interesting hint...If you zoom in - too much - the map is blended out ...It is possible that my previously described problem was simply a "zooming" problem!??! Have a great day!

I apologize, the problem was sitting in front of the keyboard....  I remembered the post from "marce1000":- To avoid browser-effects (caching, ....) , verify the issue with another browser(s). Clear browser cache, one more time.And I am happy again.....