You can login through FTP then edit the wp-config.php file and find the line: define( 'WP_DEBUG', false );. Set it to true then save the file. Log back in the admin area and you should be able to see some more error information when you redo the steps you are having issues with.
If you are getting an error message that suggests: Fatal error: Allowed memory size of xxxxx bytes exhausted, it means that you need to have the PHP memory limit of your site increased.
To do this, please edit your wp-config.php file and insert these lines:
It appears to have an infinite loop since the terms page content is created within the builder. For now, I recommend just editing your term content to the classic editor instead of the builder. I’m adding this to our issue tracker.