I'm not quite sure how to post a video on STEAM, I can only text descriptions of.

Black, high-blooded zombie, it will stand in place, and then towards you to make the movement, (it will put its hand up to you and then make walking action), but no matter how it walks can only step in place, and then after a few seconds disappear in thin air.

If you kill it before then, then it will become his corpse in a few seconds to disappear.

Then I'm using the first generation mod, the first generation of black zombie does not disappear, but it will turn into a white zombie when you get close. Every single one of them - so I'm thinking it could be a mod conflict causing this bug, but I don't have any other mods that modify zombie properties.
Or maybe mods that change ZB's costume and mods that affect loot are also considered modifications?

My paragraph is not feedback on the bug, but I hope it will help you to find out the reason why the bug is created.

Hmm, intersting.
What about conditions of the bug?
Playercount? Approximate zombie count?
server uptime?

For the 2nd issue, yeah it may be a mod that you have or something.

I just played on my server for an hour and the black to white was reduced (didn't change any settings), so the problem with the first mod might have something to do with the fact that I'm using a new archive? I remember you saying before that zombies enhance over time.
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Description of the problem with the second mod：
The conditions of the bug generation cannot be determined, the game does not report an error in the lower right corner, but the zb does disappear.
This bug only happens when you attack or get close to the black zombie, if you are looking from a distance, the black zombie does not disappear

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Zombie settings: population 1.0, peak refresh 2.0x
There are 290 mods on the server, but the only ones that directly affect zombies are the aforementioned costume and loot categories, so I don't think it's possible that they conflict with these two types of mods

No, they don't enhance over time.
Zombies in zmbmod2 are based on location(how many houses) and zombie outfit(such as police).

That's a very high pop number actually. I normally play on very high and 0.05 pop
I can test with settings like that later.

I had that same bug with vanilla game before tho.
I had pop on 2.0 1.0 1.0
Then solo in server and ran around killing zombies and eventually that happened.
I'm still suspicious that this is a vanilla bug.

I do more testing once the next stable zomboid update comes out

Well, that's all I can do, I'll come back when I find something new