Okay, I found the issue.
I did a new upload from a fresh downloaded 3.2.2 installation, but it didn't do anything.
Finally I came up to the following problem:
There was a problem with the file
It seemed that png etc did upload larger files, only jpg not.
I downloaded a fresh install of phpbb3.2.0 and overwritten the whole marc1706 directory.
Now everything works and I can upload larger files.
(has to do with EXIF data)
https://tracker.phpbb.com/browse/PHPBB3 ... ment-60413
I'm not sure why my 3.2.2 fresh download doesn't solve the problem? This should already be incorporated?