Hi,
You're welcome:)
The "Error: undefined" when saving in Helix Ultimate often stems from interactions with server-side security features like mod_security or .htaccess files, or issues with the Advanced Compile SCSS to CSS feature.
Temporary disabling of these features, renaming the .htaccess file, or ensuring the Advanced Compile SCSS to CSS option is enabled (or disabled after development) may resolve the issue.
You may check the following conversation to see if it helps:
https://www.joomshaper.com/forum/question/23933
Best regards,