EapAttributes get functions looking for 'Actual Network Name Length' in reserved bytes

Hello, I have a setup with EURANSIM+free5GC, I am trying to registration with EAP_AKA_PRIME authentication. UERANSIM keeps rejecting the incoming EAP message with response code 95 (Semantically incorrect message). The auth.cpp code (NasMm::receiveAuthenticationRequestEap) rejects the message after length-check on RAND, MAC and AUTN. On some debugging I noticed that the corresponding 'get' functions for RAN, MAC and AUTN are expecting actual length specified in the two bytes following the 'length' field. But these bytes are marked as 'reserved' RFC4187.

What am I missing?