Firstly i would like to say that there are many problems with the models of nikana zaw on both default and skin applied have the same problems which are present no matter what which also have been present in the game for a long time now (All these bugs happen to any skin of the nikana zaw i can put on a tennogen, normal or deluxe skin on my nikana zaw but all of these bugs will still persist.) https://imgur.com/a/6Ck3rCQ (Added more screenshots/updated 14.12.2019) a collection of images that show different bugs that happen on the nikana zaw.
NOTE: I should put this here that after a lot of testing and using the nikana zaw in general i have come to believe that the main problem for everything that is bugged about the nikana zaw is related or caused by its bugged sheath/scabbard which "clips" thrue the blade dosent color properly for some reason has its own identical copy of the sugatara your using and basically just dosent work correctly.
Unlike the other nikanas you cannot change the scabbard colors of the nikana zaw by changing the attachments colors separately to the hilt and blade since the main colors change the entire nikana colors and attachments only change the sugatara. (New Screenshots show this problem by comparing putting the same skin and colors on nikana prime and the zaw nikana.)
There are numerous bugs related to "cliping" of the scabbard and blade and disappearing scabbard and or improper wielding all shown the imgur album that i linked above.
Also when extracting while using/wielding the nikana zaw you will dual wielding your scabbard and sword in both hands as the cutscene of you entering your Landing craft plays and this sometimes happens in combat recently it happened after i stealth killed a enemy and when i started using my secondary i had the scabbard and the blade on top of my hands while using my pistol. (Images of this are provided in the imgur album.)
EDIT: I've added some more screenshots to the imgur album it shows me using the same look on both the zaw nikana and nikana prime same colors same skin but very different results. Putting colors on a nikana zaw is like putting those same colors on attachments as well without actually doing so and any colors you do put in attachments only affect the sugatara unlike all other nikanas.
EDIT: I also found out something else about the disappearing scabbard/sheath bug and the 2 sugataras bug if you have a sugatara equiped and if your nikana zaw sheath were to disappear the extra sugatara thats not supposed to be there disappears with it. (Which makes me believe the 2nd sugatara is tied to the bugged nikana zaw scabbard/sheath.)
EDIT: I finally found out how the scabbard/sheath disappears if you ground slam that's what causes it ground slamming makes your nikana zaw sheath disappear i tested it multiple times every time if the sheath is not already missing if i ground slam its gone completely along with the 2nd sugatara that is attached to it which is not supposed to be there since that is a related bug with the nikana zaw sheath having a second sugatara attached to it. (After a bit more testing sometimes it takes a bit for it to disappear but ground slams are definitely the cause normally i just noticed that its gone after playing for a bit but if i ground slam right as the mission begins it will start missing shortly if not instantly + another way to make the sheath disappear is to do a melee attack and aim your primary or secondary weapon before the animation ends there might be other ways but these 2 im guaranteed make it happen in general using melee makes the sheath go poof in most situations but ground slamming and "cancelling" or ending an melee animtion for example as stated above aiming your weapon makes it disappear 100% of the time while there may be other ways that i yet to know off.)
EDIT: Respawning (dying in solo or holding X in public...) makes the sheath/scabbard reappear but will disappear again if you do any of the above described things that make it disappear. (Varying amounts of success with this sometimes it dosent reappear.)
EDIT: Found another bug if you have your nikana zaw set to invisible when holstered its sheath and the extra sugatara from a different bug will just be floating on whatever holster slot you have your nikana set (for example mine is on my back and if i set it to invisible when holstered the sheath will just float on my back empty no blade in it and the extra sugatara will be there floating as well.) + This happens a sometimes when your flying a railjack.
EDIT: Noticed another bug with the sheath/scabbard any type of cloaking Loki, Ivara, Ash, Shade everything will not affect the sheath and the blade and sugatara go invisible but the sheath and the extra sugatara (From another bug) attached to it does not. (I put more screenshots with examples in the imgur album) + While i was testing i found the new sugatara (Zato sugatara) from the Excalibur deluxe set to be very jittery and unstable on some skins like the tennogen shinigami nikana one im using (this happens on all nikanas i think only tried it on nikana prime besides nikana zaw).