This is the ticket I raised: Jira
Sadly the ticket was closed by a developer because it is a bug in rclone, which cannot be fixed by TrueNAS team.
As stated in this post it might be an option to set rclones-option filename_encoding to base64 to reduce the filename length.
But I don’t actually know how to setup that for my cloud sync task 
Best regards,
AMiGAmann