Agriphila deliella (Hübner, 1813)
Larvae in a silken tube between the culms.
Molinia caerulea, that also is mentioned, does match very badly with the two previous species.
distribution within Europe
egg, larva, pupa
Kravchenko, Poltavsky, Segerer, ao (2020a), Lepiforum (2021), Wegner (2010a).