Erling is on target.
Did the dealer check for fault codes?
If it is a fuel pump issue then sometimes a fault code is logged.
One (of the 2,587,943) interesting thing that Joel said a while back is that many times hard starting is caused by a battery/charging system that is not quite up to snuff. BMW runs the injectors at a reduced voltage, so if the system voltage is low to begin with then the injectors may not be firing well. He would commonly get no-start bikes that would start without issue if cranked over while attached to a battery charger.
Since failed stators are another not uncommon issue on this bike I would check the charging system voltage.
Since the dealer has it .... Keep us posted.