Unions do not separete

As you can see in the video, the union is having an error when it is separated and when it is time to join other parts together, I need help to solve this error.

This union that I made was 4 months ago, I don’t know if Roblox Studio had any update in that time, which may have reduced the size of the parts but this is bugged.

Does anything show up in the output widget when you try separating that union?
Have you tried toggling the “Studio solid modeling improvements” beta feature and restarting Studio?

Yes, I already tried, but it didn’t work.