The modpack scripts have errors
Applies to Forge, NeoForge, Fabric, Quilt.
What it looks like in your log
There were KubeJS startup script syntax errors! See logs/kubejs/startup.log for more info
What causes it
A KubeJS script in the pack failed, which on servers usually stops startup entirely. This is a pack bug, not a server problem.
How to fix it
The exact file and line are in logs/kubejs/startup.log. If this is a stock modpack, update or reinstall the pack rather than editing scripts by hand.
Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.
Check your own log