CX agents advise me that backtrack is not allowed and a city cannot be gone through twice, no matter it is a stopover/openjaw or transit. My itinerary is:

NRT - FRA (o) ZRH - HKG - LHR (stopover) - YYZ (stopover) - LHR (transit) - HKG (transit) - KIX

Approached 10+ agent but to no avail. Really despair !