I just figured this out. So, I had the same problem as alot of other people where Id set an original object to not spawn at start so i could interlock it, only to not be able to get it to respawn. Well, im sure alot of you have already figured this out, but this is to help those who haven't. Simply find the teardrop from your missing piece, highlight it. That will give you the option to set it back to yes on start. Then all you need to do is start a new round. Saved me alot of time recently.
I figured this out when I was trying to interlock OLN objects too. You have to have the object(s) on force spawn for you to be able to select the teardrop.
If you count listening to the new It Dies Today cd while forging, then you're quite accurate. YouTube - It Dies Today - Thank You For Drinking