Hello!
Could you check your /var/log/httpd/ file for the error - more information about why it’s a bad request should be there.
Also, I did some digging and found we have seen a similar issue before, and there’s a topic on it in Discourse. In short, you can decrease oidc_state_max_number_of_cookies (read about that here) to significantly reduce the prevalence of this error. There is also another user at the end of this thread who found a solution by configuring the header field size limit in Apache and creating a file for nginx - we haven’t tested this solution ourselves however.