I have had similar issues with more than one of my Harleys. Slowing up for a stop light and cannot downshift into low. Hung up in second or third gear. You could beat on the lever with a hammer and get no where. The only way out of the problem for me at the time, was to rev up and slip the clutch from a dead stop and chug across the intersection and then the damn thing would operate OK. Happened to me 5 or 6 times over the years.
Now it has also happened to me on "up" shifts............but that was my fault. I bang down on the heel shift lever to upshift and occassionally did not raise my heel up far enough for the lever to "ratchet".......thus no shift on the next try.
Not at all sure that the down shift problem is created in the same manner.