DaemonUmbra

For the love of... do you have access to the server's files? If so go into the logs folder and get the debug.log file

That's not a debug.log from the server.

That's not what I asked for...

Just get debug.log from the logs folders of both server and client and upload them to a paste site

https://minecraft.gamepedia.com/Minecraft_launcher#Installations

Please don't necro old threads, if you have an issue make your own thread.

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

Please provide your installer log (more info in my signature below)

We've had people report this but we've been unable to reproduce it ourselves. Could you please share your hardware specs, and your java specs (version, vendor, etc.)? Edit: Also, can you reproduce this issue on the standalone launcher without Twitch?

Please provide debug.log using one of the paste sites in my signature

One of those logs is edited and the other isn't a debug.log. Please post unedited debug.logs from both server and client.

Please provide your debug.log using one of the paste sites listed in my signature

1.12 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.

1.12 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 don't Necro old threads. If you have an issue make your own thread.

You did install a Forge server, right?

It's as if a clean shutdown is the INTENDED way for the server to shutdown! If you kill the server process WHILE the server is saving you are likely to corrupt the world. Also shouldn't you be using screen for things like this?

Please don't download files manually.

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

You would be best off writing them from scratch. Know that if you endeavor to do so you will find no help here. Around here we move forwards, not backwards.

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

CurseForge is the recommended site for mods. As for that error, you shouldn't need a JDK, a JRE should do. I'd recommend getting a Java 8 JRE from here, click here for a direct download of the MacOS version.