• IAEAddonEntrypoint improperly says the common initializer is still named appliedenergistics2 while it's ae2
• By the time ae2 triggers, it is too late to register parts with PartModels.registerModels as it's already frozen. A temporary workaround I found was to trigger my initializer at the end of AppEngBase#<init>

I'm pretty sure these issues are exclusive to Fabric since IAEAddonEntrypoint's not used on Forge and Applied Mekanistics registers P2P tunnel models with no issue

Which version are you targeting? 1.18.2?
(I know this probably exists on multiple versions but recent registry changes make it a bit more touchy)

1.18.2, well 11.0.0-alpha.3