Yeah. Lots of trouble. They will cancel the whole ticket when you no show for the first leg. If it's only showing availability starting in YUL, it is married segment issue, meaning that Lufthansa isn't willing to release the seats to passengers out of JFK.
Passenger traffic is up about 10% y/y so with supply not increasing fast enough you will see less availability.
Keep checking and be flexible. LX releases J space a couple of weeks before flights.