This just confirms what has been stated in this forum many times (and will apply to most other carriers as well). Phone agents will or can not touch award tickets issued by other carriers and will keep suggesting you to contact the issuer of the ticket for rebooking. This applying even if IRROPS occurs after travel has commenced and despite that the operating carrier is supposed to handle it; this is simply how it works and there is no point in calling LH have this fix - not going to happen! Only agents at the airport will be prepared to solve IRROPS - like it also happened for the OP. So in a situation like this you either call the issuing carrier or go to the airport on the day of departure to have it solved.

The agent should have rebooked you into I class but was either sloppy or didn't want to spend the time getting I class inventory released to you so he/she just booked you into whatever lowest available revenue class. You should be happy as you will now earn miles/points for these flights!