You can delete this post if i am wrong but i think the modpacks take alot of time to start within servers so like over 5 mins but the problem is that when the server starts starting the timer for when it will automatically will too and with vanilla servers its no problem because regular servers don't take 5 mins to start but because of the 1100m of ram the big modpack servers take more time and it stops when it hasn't even started so my suggestion is to
1.add more ram to modpack servers
2.give more time for modpack servers to start
3.take away the modpacks over 150 mods
And if i am wrong about all this you can call me a fool and delete this post.