Thanks for the answer, now I know that they are working on it and it is not my computer related.
I have swiched to Edge, but same problems, than to Google Chrome and the checker does work again. But my stats page Challenge tab still only gives the list of challenge caches that I have foound and fullfiled and is still circling and rotating on the results of challenge caches that I have found but not yet fullfilled.
I'll keep an eye on this forum and hope the bugs will be killed soon.....