block disappears in edit mode WP

It is a great plugin, works easy, I have one problem.
On one page, the block which is animated, disappears in the “edit mode” of WP
but on the front end it is OK! (but you cannot see anymore what you are editing).
If I copy this block to a new page, the same thing happened, including for new blocks on that page
I use Chrome, tried to clear the cache (Ctrl+Shift+R) , tried another browser (Firefox), no solution.
It might be solved by re-creating the block (again, other pages are working great) but I like to understand the problem and have a solution in case it happens elsewhere.
Do you have any suggestions??