Hey,
Update Builder's Utilities, it doesn't work on 1.12 servers and it only works on
1.8 the one we currently have I believe.
Here's the link for Builder's Utilities (it has a "Download for 1.12 and below" button):
https://www.spigotmc.org/resources/builders-utilities.42361/
Thank you for taking your short time reading this.
Sincerely,
- Narpzy