Russian language

Hello, since last update plugin stop to serve any fields with russian character. if at least one field contain one russian character – whole form does not saves. My old form did not stopes to work, BUT – after submit the form there are an error “an error uccured, please try again later” and i can not to edit form – nothing saves. In spite of this error e-mail sending successfully.
p.s. Similar problem was with the essential grid plugin after wordpress updated to 4.2., they used ajax and during saving ajax gives back an empty response

https://wordpress.org/plugins/smart-forms/