Unable to serialize value. Error: Malformed UTF-8 characters, possibly incorrectly encoded for some url-key

my website has been running for while and the url key for some category have been using for long. but suddenly some category pages (most others are still valid) referenced by url-key.html not working. the backend report show

Unable to serialize value. Error: Malformed UTF-8 characters, possibly incorrectly encoded

i tried to delete the url-key and give a new one, but not successful. there is error also.

do you have any idea?