I just made another topic regarding corrupted save files where I described this bug, but I managed to reproduce the bug and given that it probably isn’t directly connected to file corruption, I decided to make a seperate topic about it.
There’s a way to make a NegativePart all parts unselectable if you union and seperate negative parts in a few specific steps. I attached a file below which I used to reproduce the bug. So, here’s how the bug works: open the file I put below and expand the workspace. Then, select the first NegativePart and then shift click the one at the bottom to select all of them. Then press the Union Selection button. You should now have one big negative union which is selected. Click anywhere in the scene to deselect the union. After that, select it again and press the ‘seperate parts’ button. Now, click somewhere in the scene once again to deselect all selections. Now repeat the first step: select the first NegativePart in the workspace and shift click the one at the bottom to select all of them. Then, once again, click the ‘union selection’ button. Now you should get a big negative part once more. Here’s the thing: if you deselect the negative part and try to select it again in the explorer, it won’t be highlighted in the workspace, which is really odd given that the big negative part could be selected from the explorer the first time it got unioned together. In fact, this is now the case for any part in the explorer. You can click them in the explorer but they won’t actually be selected and highlighted in the scene.
Edit: @Mister_Mystery correctly pointed out that this is the case for all parts, not just the negative parts.
PleaseCorrupt.rbxl (21.4 KB)