DaemonUmbra

Yes... that is not our concern. We don't provide support for 1.12.2, the fact you have things tied to it does not change that. If you want support, update. If you want to stay on 1.12.2, you're on your own.

Do you know what a NullPointerException means?

Do you know Java? Are you capable of looking at the code you're trying to use and fixing your own problems?

Forge has nothing to do with shaders, that's on Optifine

Show a screenshot showing the PlayerEntity class with the private capabilities

Recreate the issue and provide debug.log from both the server and the affected client using one of the paste sites listed in my signature below.

Pastebin or one of the other sites listed in the "Logs" section of my signature below. and the installer should make its own log in the same folder as the installer, with the same name as the installer but with .log on the end

Try providing the log

Well the next step is a binary search (google it) to (hopefully) find the problematic coremod

Yes

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

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

To me this looks impossible without coremods or mixins screwing things up, what mods are installed?

Merged your replies to the other thread into this one, please don't hijack other people's threads and then act like we're assholes for asking you to make your own thread for your separate issue.

Show a screenshot of the file that gets downloaded, please

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.

Are you trying to make a config or do you have the config made and want to enable the config button?

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

The config button is enabled when you register a config gui, there isn't a default one anymore

Screenshot?

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

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

Remove Optifine