In a build with 1328 mainly very small pieces that are buried within each other
EDIT: After digging through heaps of code I found the type of missing piece. Then I had to count each and every one on the physical model and compare it to the digital one. I found it, good thing it was external and easy to spot.
EDIT 2: Now every time I open the file that damn piece gets removed even though it’s been rendering properly for over a month now.