I haven't tested this in awhile so I forgot it was an issue I was having, but tried it today, and still the same case.

ProjectRed Version: I tested it with 4.9.2.101 and also compiled it myself, still getting the same issue.
https://pastebin.com/wg8nHh15

There's also a line at the top of that Pastebin which may or may not be important with this.

The access transformer is not being applied. Any reason for this @covers1624? Its included in the build script and seems to work for everyone else.

Not sure.. Buildscript looks fine to me, should just work.

I tried ProjectRed with no other mods. Only mods being CCL, FMP, MrTJPCore and PR. This is the entire log instead of just the crash report, I'm not sure if it will help at all, though.
https://paste.ee/p/JNdES

Oh you are using the -all jar from maven. Dont do that. You need to use the module jars.

Oh. I didn't know that I shouldn't be. I mean, what would the difference be anyway apart from -all jar containing Relocation, which in this case though, is the reason it's unfortunately crashing.

Alright, that's fine.

It doesn’t have everything needed to work. Don’t use it.

Try it with just ProjectRed installed and see if you get the same results. It might be an optifine conflict.