Error thrown Using $this when not in object context

hi!

i have an error in saving a product
https://derkleinehofladen.at/wp-admin/post.php?post=1356&action=edit

Error thrown Using $this when not in object context

i do not know why this comes I changed nothing only updates everywhere?

know anyone why?
thx
Peter

The page I need help with: [log in to see the link]