@kenami
@ProvenData
@ittrgrey
@Deemsx
@PeZsmistic
This is due to ChildData missing from the union. PhysicsData remains afaik, but, when ChildData goes missing the Union will be separated into nothing (there is no instances stored for it to separate into), and will appear “invisible” despite having collision. I think additionally MeshData is lost? I don’t remember if MeshData is or isn’t lost… (These are all internal properties of PartOperation & PartOperationAsset instances, the latter being the instances stored in the Roblox cache for downloaded union content)
The reason that copy and pasting sometimes works is because the union can still have an asset ID with it on the web which will have old content. If your restart studio and save the game though, I’m fairly sure this ID gets overwritten because it gets uploaded as a new asset.
If you guys can provide me rbxl and rbxlx copies of effected Unions, I can possibly look into a way to recover or repair them hopefully. The more the better, but, it may not be possible as the data may just be gone entirely, we’ll see I suppose.
Also, if you have unions go missing in your place and its published, go into Game Settings > Places > (Sub menu) > Version History, you should be able to find old versions of your Unions still in tact there.