Why do I keep on getting this crash report?! Forge loads mods in parallel, and whenever Java is requested to load a new class, a "Mixin" subsystem is initiated to compute injections and/or redirects, ...

I made a fresh modpack, put just create and TFMG in it, and it worked fine. I try to bring it to another modpack, with just some config files copied over, all other mods disabled, and I get this error ...