I tried out the c2me-fabric-mc1.18.2-0.2.0+alpha.7.9.jar build on 1.18.2 and everything worked fine. I then tried to run 1.18.1 with the latest compatible CM2E version - c2me-fabric-mc1.18.1-0.2.0+alpha.6.55-all.

The game crashes on startup with errors from ARRP.

The same applies when trying to run c2me-fabric-mc1.18.2-0.2.0+alpha.7.0-all on 1.18.2 or any other previous version of C2ME on any version of Minecraft.

Deleting the c2me.toml file in .\config fixes the issue.

It seems like alpha.7.9 writes something to the c2me.toml file, which then makes it incompatible with any other previous version.

To reproduce, simply run the game once with alpha.7.9, then try again with any other previous version of C2ME.

This is currently working as intended as we changed the config structure and have protection for mismatched config version.

Yeah, but that also means if I want to switch to 1.17 (or other), the game will crash. Unless it is planned to backport the latest iteration, or for it to use different config file.

If that doesn't happen, lot of people will come here to report related crashes.

A warning has been added in README for this kind of crash. This is not fixable as we can't modify the released binaries.

Closing as wontfix.