iR80

I do have mods on my KSP install like Mechjeb but I won't use them. Just to let you know.

I'm actually doing something kinda like that, except I'm randomly attaching them to one another using claws and adding more claws to help keep them together. So far I've got 4 asteroids, but I don't have enough E class asteroids. I might throw in a comet or two but comet physics are wonky

If you've ever flown a spacecraft within a certain area of the location of the launchsite then I think the game automatically unlocks it, but I'm not entirely sure since I don't play Career mode, only Science mode

I'm gonna try this anyways

I hope KSP 2 actually supports merging asteroids to make bigger asteroids. I'd actually try to build a planet bigger than Stephenson 2-18 just to see what'd happen

I don't know why, but I honestly thought you could do that in stock KSP, but I guess not Time to build a giant wall made entirely out of asteroids around the KSC to protect it, i guess

Sometimes for me, when I undo the placement of the vanishing part it reappears.

I'm just curious, since I have a few asteroids that I've mined, but I don't know what I should do with them

That's happening to me too, but with any part attached to a multi-coupler or engine plate. I have a feeling it may be ClickThroughBlocker or Toolbar Control because I also have those mods on my KSP 1.12 install. Edit: I tried removing both mods but that did not work. It only seems to occur with stock parts, because modded parts work perfectly fine.