Yes, we’re having the same problem. My moderators were all confused about how this was happening, and then I discovered using incognito that “hidden” doesn’t really mean hidden in the removed sense, as we would have thought, it just means collapsed.
And the problem was discovered because we had several user replying to the original hidden post debating about whether it should have been hidden. This led to a total of 7 hidden posts in a row.
My takeaway is that if our mods want to actually remove a post their action needs to be to delete not hide it.