Alright, I don't have exact dates of conversations and realizations but the story I heard...
The contractor for the module line for months was "we almost got this it's fine just a bit more time" which is typical from a failing contractor. It wasn't until Elon being his micro manage self went down there and gathered some heads for chopping did Tesla realize holy *sugar* you guys really don't have this. The cause was a bit of classic Elon hubris as Tesla not only wanted the most automated line but also with a very small footprint. You ended up with overly complicated machines that they couldn't even get the programming right for. Anyways then Tesla takes over and their guys think "well I'm sure we can work out the last few kinks and get this *sugar* running". Some time goes by (not entirely sure how much) and they realize holy *sugar* we have to start from scratch. They pulled Tesla people into the project but also hired outside help to redo the whole programming of the line. Which Elon openly talked about. The outside help was not Grohmann as they were working on building a line from scratch, robot and programming wise, in parallel in case Tesla couldn't get the original line to work. With Tesla staff and outside contractors working 12-14 hour days 7 days a week they got the original line working.
This is why the DOJ investigating a company for missing a production rate by a measly 6 months is asinine. Any large company has many groups saying many things, translated by managers trying to look good, getting telephoned up the chain. Not even taking into account Elons honest and optimistic nature. It has to be massively obvious deception for it to be CRIMINALLY (DOJ, beyond reasonable doubt) proven in court. This is why you hardly ever see the DOJ look into *sugar* like this, except when it's Tesla apparently.
Anyways, that was the major factor for the delay as I understand it so unless they are looking into something else, from what I heard, the whole thing is a distraction.
/End rant
Not an advice
blah