Hi Peter,
the problems with the (contact) Forms functionality are being looked into (and addressed) by the people at Rapidweaver. Check out " Elements Form, missing resources" on this forum, as an example.
Lots of tips, who knows some might help you (too) ?
I did not try the Elements-Form at Strato, but with another (part of the same German) provider: Ionos. So far I did not get it to work, but YMMV.
Bart-Jan.