I am working with a Late Ketland lock from Chambers. The frizzen has trouble flying all the way foward and exposing the priming powder to the spark.
Try this first it will not hurt a thing.
If this is a new lock, they work better when they are broken in and have some use; the frizzen face even though the correct hardness may still need to work harden a bit. Sometimes when new, the face of the frizzen is a little rough catching the flint. Mine at times tended to catch the flint at the chatter marks and would not open fully at times.
I simply polished the face of the frizzen with some very fine emory. This provided a slick surface for the flint to slide easily but still provided good spark.
This lock, mine at least, tended to be real sensitive to flint length. Too short and it would not fully open, too long and it would not fully open. Most of the time it did not open was due to the flint being too short. Simply moving moving the flint forward in the jaws just a little solved the problem.
In my experience bevel up or bevel down tended to depend more on the overall shape of the flint and how it ends up in the jaws tightened up.
If no luck with simple adjustments and polishing, you may want to pull the frizzen spring and make sure she has no binding at the frizzen pivot screw. If it does have a little drag when you manually flip the frizzen with your finger, you may need to remove the pivot screw and polish that area just a little.