Please note that longbow #4 only has a range of 900 and longbow trait adds 300 to the range. The other skills have a range of 1200, which makes it 1500 except for #4.
I also do not have the issue that you mentioned as I always use the red ‘out of range’ warning on skill 4 as an indicator that I’m above 1200 range to inflict max damage with #1 (max damage at 1000+ range). My skill #1 still will still auto attack between 1200 and 1500.
The only time when it does not auto attack and still hit the enemy is when I’m over the 1500 range with Piercing arrow trait (not sure if trait is a factor) as the arrows keep flying over 1500 units. This is indicated by the red out of range bar at the bottom of the skill #1 box.