I have done the same things too. It is strange really why it is not working for me for some civilization units.
Apart from this, there was a problem with my mod update which the mod title and mod descriptions were not updating. After that, I made ticket to AOE4 support and thy fixed it. Probably, I might have a similar problem for this issue too 
I try to produce the Mongol Great Trebuchet and again I get the pre-cached red box model error.
For this cool unit:
Age of Empires IV huihui pao
But when I try to add it to my mod, I get this 
I have tried to replace the model of siege weapons, and then there will be this kind of model dislocation.
What is the name of this weapon from French? thank you.
Spear model of France (charging / approaching the enemy).
@ahioz9426 I think it was a specific bug for that HRE spearman infinite corpse unit.
With normal HRE spear Age 1-2-3-4 versions, it worked^^:
I am really happy now (for 2 days I was trying this things)^^, thank you for your cool guidance friend.
@ahioz9426 is it possible to add a fire effect on the Mangonel, Trebuchet, Springald projectiles? It will be something similar to AOE2 siege weapons that throws fire - incendiary stone bullets or arrow etc from siege units.
This is the melee weapon model of the Chinese knight.
It can be realized, because I have seen this kind of mod in my impression, but I don’t remember which one it is, and I don’t know how to operate it.
They said we can customize the unit models very soon.
Can you describe in detail what it means to customize the unit models?
Can the model be modified through 3D software, or do they add a special function / window to modify the model, which can be changed at will like the skin of other games?
I always hope to easily change the parts of the unit model, such as helmet, clothes, shoes, arrow bag, shield, mount and so on.
Chinese scouts also have a sword with a unique appearance.
It should be nice if we can add a logo on units and buildings and ships’ the shields, flags, badges etc. We should bring up this to developers really.
If AOE4 developers provide a way about how to remodel the skins / models of the units with 3D Software, it will be really nice concept.
I really want new civilizations like Turks etc too. As historical, it will provide a vast gameplay in every meaning from Middle Asia to Anatolia, North Africa, Middle East, Balkans, Black Sea, Europe etc all regions. Thus, I really wonder how will they describe and implant the Turks Civilization in AOE4.
you are the best^^. these pictures helped me a lot
I have finished the Chinese Civilization today and I updated the mod in the game too. I wanted to share it with you too.
The Great Wall is really nice. Really nice siege experience while defending^^.
This thick wall looks very amazing! I’m going to experience it in the game now!
And I suddenly had an idea. Maybe I can suggest the official: the Great Wall gateway can unlock the construction of a thicker wall for Chinese, just as the sparskaya tower of Rus can unlock the construction permission of the stone wall.
I have applied The Great Wall to Chinese Civilization. However, there is a small problem; because of the game mechanic for this wall while it is applied to Campaign only. It is not flexible like the normal walls we build. You need to make a SQUARE concept like a fortress or a straight line.
The Great Wall is really nice and big. Thus, I increased the HP, cost and build times for these objects.
After that I wanted to use normal Chinese Walls via Chinese Wood walls / bastion / gate which I repeated what I had done for Russian Civilization to make Russian Civilization to have stone walls. However, I realized something while doing lots of testing. When you change your wall concept to The Great Wall, the stone wall bastions and wood bastions are using the same bastion parent data model, so I couldn’t add that flexible Chinese Stone Wall Bastion to wood based bastion model exchange.
At my mod thread in the AOE4, I had explained the problems I experienced while applying this Great Wall, it seems like developers made some small limitations. Once you get used to this Wall construction method, it is quite fun to build the Great Wall. Your defense siege experience become totally different in the gameplay really^^.
I wanted to add Kiev Walls to Russians; instead of west style; but some models are hidden that content editor doesn’t let you build, it is same for Wolf Monument etc too
Maybe this can only be realized by the official. Can I quote this picture you sent?
