I think an issue from ~8 years ago is unresolved:

it seems to me that this template contains labels form the neuromag306 system. Is it right? And can I find the template somewhere?

Locally load neuromag122_neighb.mat shows:

>> neighbours

neighbours = 

  1×306 struct array with fields:

    label
    neighblabel

So this still seems to be an issue.

Apologies if this file is no longer used -- we use it in MNE-Python as a definition for neighbors and a user hit this issue. If it's not used anymore by FieldTrip, another option would be for us to stop using the file and use a Delaunay triangulation instead at the MNE end.