Sorry for your troubles so far.
Please let me know more details,
Does the page give the message “are you sure you want to leave? etc…”?
or Does the blocks grey out after you add a new one “after dragging it from the top panel to the bottom editing panel”?
What WP version are you using.
If possible please allow me a temp admin access so that I could create a new page and try to replicate the issue.