Error 400 after modifiacation of the content

Hi there,
When I have the plugin installed and I go to a product and make some modifications and save it, the page sends me to an HTTP ERROR 400.

I have to reload the page and sometimes it moves me to the login page and sometimes returns back to the non-saved page.
Generally, the plugin works well after some CSS style modifications.
I do not want to delete it because I like it and want to use it in the future and I paid money for it.
Will you refund me if you fail to find the culprit of the issue?

https://www.screenpresso.com/=bgJAg
Regards,
Eugene