Hello EB,
no i didn't try any other avl server and i didn't try it on older firmware, as my rutx11 is new and one of the first steps was a firmware upgrade.
I would expect, that all points are measured and send in a row positioned over a road, and not like taking the short way through the air ;): see the screenshot of GE along.

So i think, that the avl data could not be sent, perhaps no mobile connection for a while. But the router does not prove if the connection was successfull, just lets data drop. This behaviour remains through all days.