If I'm permitted to do some wild guess, the problem you are facing does not rely within Method::Signatures nor Function::Parameters but with Moo on it's own.

Moo does a lot of code generation and a syntax error makes everything go messy.

Also compiletime/runtime timing must play a role in this: as you discovered perl -c Moo_with_syntax_errors_module.pm reveals the right point where the error happens: 'Bareword "nnext" not allowed.. '

I'd try to change use module into require module or using Module::Load as side experiment.

I hope this can be useful for you even if my English is easily misunderstandable and my OO experience is very very limited.

See also this Moo report

L*