Does this happen with *new* styles you’re adding, or only with styles from a prior version of the plugin?
I’m aware of an issue where styles that existed before the upgrade had extra slashes (WP added them to form data). They can be removed using an online tool like this one:
But that won’t work if the slashes are added on each save.
Can you can send a login using the contact form? I’d like to have a look.