Its part of the class gauge system....summoner has moments like that as well where you have 1-2 seconds of trance left and go to do a Deathflare only to have the animation cancel out before the blast because the timer ran out before the animation finished.

Gauge-related mechanics that were previously normal buffs that could 'drop off' had a second's worth of leeway in the old system, but the new system is much more strict. Basically you need to learn to not push the wire because the system won't let you anymore :/