How was that diagnosed? I'm hearing that some shops have software to diagnose some issues with di2.

With a Shimano SM-PCE1 most likely. If your LBS is up to speed, they should have one.

Now I'm very confused. I posted earlier that my di2 was ghost shifting from the large chainring to the small ring and shifting around on the back too. The problem on the front rings got so bad over the 8 miles this was happening before my chain broke that I had to shift the chain back into the large chain ring once every 50 yards. I put a new chain on it earlier this week and now everything is running smooth. No problems at all. Is it possible the problems were the chain only? I had been riding the chain that broke for weeks with no signs of any problems.

Any and all sage advice welcome!!!

Yup. You probably had a bad or stiff link.....or perhaps you used a quicklink and either installed it wrong, or used the wrong type. And if all of this was done by your LBS, then they've got some "splainin" to do and you need a new LBS, or learn skills yourself.

I'm having a similar issue! My FD is shifting down to the small ring by itself. I've looked online and I couldn't find any information on it.

Looks like your Di2 and use of apostrophes could both use a little fine tuning! ;)

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But how could a faulty chain cause the di2 derailleurs to shift?

Technically, the front derailleur is not shifting, but simply lacks sufficient force to prevent the chain from derailing onto the small chainring which also indicates sub-optimal alignment/adjustment. Is the front derailleur installed with the small metal backer plate that is designed to increase stiffness of the derailleur?

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Yeah it has the plate mount. All evidence now does seem to point to the chain causing the problem. I've had a new chain and ridden several hundred miles with no issues whatsoever. I guess what is throwing me off Is I would shift up to get it back on the bigger ring. If the chain forced the derailleur over wouldn't it not have the range of movement to make the shift, if it didn't shift down to begin with? The chain was moving around on the cassette too.

All of this could be caused by a faulty link or pin that worked fine until 85 miles into a race?

Thanks for the help and insight!

I had the similar issue and also dropping the chain especially when I back pedaled. I took it to a different bike shop. The Shimano rep happen to be there. He looked at my chain which I had the just put on at the other shop a month earlier. They apparently sized it too short and it had used two quick links. He adjust the limits and we got it shifting good. He recommending no quick links. They can cause alignment issues. I had liked the quick links for cleaning. Five rides since and it is shifting perfectly. I will get a new chain with no links prior to racing starts. I hope that helps. I would not buy another bike without DI2 and this is the only issue I have had in 2 years.