I have read this:
It's what happened to me with conflux shoul forge. I have rise two lvl without going in the game and now I have a sword with lvl5 but no lvl4 ability.FIXED <span class="ev_code_PINK">### Some Dynasty weapons never gain or loose abilities when leveling up.</span>
by PaladinOfMM: It seems that gaining enough experience to gain two or more levels for a Dynast Weapon 'jumps' the corresponding ability (screenshot).
It's marked as fixed, but my Dynasty weapon still haven't had lvl4, how can I reset it so I can get it up again or how to activate lvl4?