So a while ago when I was building, I was making a door through a cylinder part. I negated another part through it and unioned it. The was clearly a hole through it, but it wouldn’t let me would inside. At the time I was working with another builder and he said for me to just turn can collide off on the part and then build around the cylinder.
Today I was making this tunnel corridor thing and the same issue occurred. If you aren’t sure about won’t I’m talking about, look at this: https://gyazo.com/76e893c3bec0fdea34d8afd37e3a336e
This only happens sometimes though but I’m not sure why.