3D-Polygon: Edit features -> Add vertex does not interpolate Z, Z of new vertex is 0m

[FedericoFossatti86]

Hello,

I am running ArcGIS Pro 2.8.3.

I need to densify some 3D polygons by adding a vertex to segments that are longer than 50 m.

The problem is that when I add the vertex with Edit Vertices -> Add vertex, the newly created vertex will be at z = 0 m. I want it to be interpolated using the Z of the nearest vertices. I believe this is the intended behaviour of ESRI:

This is my original polygon (the format is shapefile by the way):

I want to add a vertex here:

And I get the vertex with z = 0m, instead of an interpolation of its neighbours:

Any clues?