DaemonUmbra

Are you also trying to replace your version in mods.toml?

If there wasn't one in defaultconfigs then deleting it from your serverconfig should work, just make sure you get the right save because server configs are per-save when it comes to single player

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Please provide debug.log (more info on where it is and how to provide it in my signature below, just expand the spoiler)

Oh right it won't repair server configs with the way they work now, take jumbofurnace-server.toml from the defaultconfigs folder, go into your saves folder, into your save, and put the config in the serverconfig folder there.

If you have the same issue, did you try the same solution?

It appears to be what I'm looking for, but it still looks incomplete. Are you sure you posted the whole file?

Did you set it to require a tool? Also I recommend NOT setting things up this way, as it makes things inflexible, set the properties when you invoke the constructor rather than in the constructor itself.

Please provide debug.log (more info on where it is and how to provide it in my signature below, just expand the spoiler)

Remove OptiForge and Optifine

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Try running the modpack without Twitch (a video on how to do so can be found in my signature below in the Logs section, Twitch Launcher subsection). Or try with Overwolf's beta Curse App, initial impressions are it seems to work better than Twitch.

Back up your saves and repair the modpack

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Delete the forge-client.toml config file

1.7 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Please provide debug.log (more info on where it is and how to provide it in my signature below, just expand the spoiler)

How did you install the modpack on the server?

That debug.log doesn't match, but that crash log is saying that a config file got corrupted, replace it with the configs from the original modpack files

The amount of data loading exceptions in this log is disgusting. Remove Engineers Tools, start the server, stop the server, and provide debug.log again

Thank you for not stubbornly refusing to try removing Optifine, you don't know how relieved I am that you didn't make a deal of it.

Remove it and try again

The general process is literally just to update your version numbers and dependencies, and fix compile errors.

As you were told TWICE in Discord... we only support 1.15 and 1.16 at this time. Update to receive support.