Hi Sascha,
I just tested this, and for me the form sent successfully.
Has this been resolved?
Just a note, always updating IS a good idea, but you should only update one thing at a time. For example, only update one plugin, then make sure the site is still working, then you can move on to update another plugin, and so on. If you update many things at once and then something stops working, it's harder to figure out where the problem came from.
Please let me know if this is fixed.