I think that's what Musk alluded to in the shareholder call. Two parts of the battery pack assembly line were supposed to be up and running by now, and the contractor really dropped the ball, so they have to redo all the software/hardware themselves. Naturally the hardware aspect is going to take more than the software side, and I wouldn't be surprised if that's why they purchased that other automation company. I also wouldn't be surprised if that's why their directory of battery engineering left.
In terms of parts stacking up, having an inventory of parts gives them more leeway if they have problems with individual part lines later, and they can also proactively look for problems by running those lines at or near full speed and fix those before they're an issue.
Edit - I guess they're getting more than one part per press by switching out forms, which explains why they would build up parts inventory.
https://www.reddit.com/r/teslamotors...tions/dphj9x8/