A friend had a ticket DOH SIN DOH. The DOH AUH DOH flights were in J. The AUH SIN AUH flights were in F. It was one ticket. As she had a stopover in AUH on the return to DOH, she was not allowed to use the F lounge. To use the F lounge, she must have been on a connecting flight and not on a stopover. It doesn't make much sense to me.