This seems to happen if the player has not used ADS in some time after multiple stance transitions/sprinting. I notice this happens especially when in full sprint and having to stop to ADS at the same time (very common in DayZ as players often jump out unexpectedly while you are moving).
The general concern can be replicated if you simply enable Toggle ADS and press/release ADS right click multiple times. The aim will get "hung" up and the client does not know which transition of aiming it is supposed to be in. You can often get the ADS to basically hang or even do hip fire ADS even though Toggle ADS is enabled. It very strongly looks to be that since you have the hipfire daisy chaned to the ADS code and must go through that 1 second hipfire transition to get to ADS it will get stuck or lost in that transition handoff.
I STRONGLY suggest building in a separate ADS mode that does not rely on script piggybacking of the hip fire action in order to simply raise the gun ironsights into your line of sight.