I'm trying to book a business class award ticket from Boston to Nairobi via Frankfurt on Lufthansa on April 3rd. I'm planning to either use Aeroplan or LifeMIles (Lifemiles preferred as I have miles but their website is a pure mess and call center unavailable). When I search for this ticket on Aeroplan or LifeMiles (or ExpertFlyer), it says there's no business class availability on those dates (April 3rd from BOS - FRA and April 4th from FRA - NBO). However, when I search for the individual legs separately i.e. BOS - FRA and FRA - NBO, it shows availability on all the programs. Both legs are operated by Lufthansa. Obviously, it also costs more to book the legs independently.

Please anyone know how I can get around this? Seems to be a Lufthansa issue hence my posting on here. Thanks!