Since some weeks I read on dewiki and the German page "Forum" on Wikimedia Commons complains about a very unstable UploadWizard. Users are very frustrated because it is for some of them (not all!) impossible to upload more than 1 image at the same time. And it seems unpredictable under what circumstances the upload of more image fails.
Personally I am uploading via LightRoom which works well, other users using the Commonist do not report any problems.
Today I tried to find the error or at least the symptoms. I can confirm that using Firefox 72.0.2 it is nearly impossible to upload more then 2 images ot once.
Firefox console shows a hint:
Request from - via cp3052.esams.wmnet, ATS/8.0.5 Error: 502, Next Hop Connection Failed at 2020-02-11 08:20:15 GMT
I am not sure if this is the real error of the symptom of another error.
Anyway: Something should happen very soon otherwise we will loose users/photographers.