@Radltruhe
haha No worry. Perhaps Steam wanna make the button that changes the color when it's "subscribed"

Oh Sorry, I just realised, that I misread the "Subscribe" button as "Subscribed"...

@Radltruhe
I 'm more like just an asset creator than a modder so if there's something from the patch causing it, I don't know how exactly I can help. But your error looks like caused by not subscribing to this prop.
This may help you understand your error?
http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=463645931
Just go down to Workshop assets and find "Unknown prefab" section.

Yes Khrysler, exactly.
I think this problems were caused by the autosave feature from assets.
In one of the last patches CO split up automatic saving to in-game and in modding editor options.
It's no off by default, but there are lot's of existing assets out there with problems, and I doubt CO can handle this with an an automatic workaround by mapping filenames in assets when the game detects there is a unknown prefab situation. So I thought it could be resolved within the prop. I am no modder at all, so I have no clue about asset modelling.

@Radltruhe
Perhaps you have Darf's building using this fire escape?

Hi,
Unknown prefab: 962814787.Fire Escape - Top (White)_Data, occurs in 624554873.
Is it possible to add this?

@Darf
Welcome! Glad that I can help on your buildings :)

Thanks so much for these! I Will replace some of them on my buildings with a white facade!