To try to figure this out:

Even though you don't need it that soon, try to see if you can come up with LNFable rates for closer in (say, a month or two from now). If so, see how far out you can get LNFable rates, to see if it's an issue with your specific dates or if they simply cut off a particular amount of time out.

Also, if you're not aware, try doing your rate searches on Saturdays. Some third-party sites now only make discount rates available outside of business hours. But between LNF's 24-hour window for accepting/rejecting your claim, and world time/date differences (are they counting business day of where the hotel is, or business day of where the booking site is based?), Saturday is the safest day to look for (and especially submit) LNFs.