unknown free variable error with fun_prop

Stream: mathlib4

[Ruben Van de Velde]

Adding the fun_prop attribute to Path.truncate_const_continuous_family (Mathlib/Topology/Path.lean) causes unknown free variable '_fvar.105131'. Anyone have an idea what that means?

[Robin Arnez]

That probably means a bug lol

[Robin Arnez]

Not sure where it's coming from though