Registered users cannot update their profile

Sometimes registered users cannot update their profile in the front end, especially if they try to change their password. When this occurs, the user receives the error message “An appropriate representation of the requested resource could not be found on this server. This error was generated by Mod_Security.”
Our website is at whitesideancestry.org and currently uses Joomla 3.9.5 and Community Builder 2.4.2.

The error tells you exactly why it's doing that. mod_security is blocking the request. You'll need to contact your host as it's likely just a false positive that they'll need to add an exception for.