As an update, I went out yesterday and it was still stuck in the small ring, but if I shifted down at the back while simultaneously shifting up at the front I could get into the three smallest cogs, overriding the anti cross chain built into di2.
I recommend plugging it into a PC and to do a proper diagnosis via the E-tube software !
It might be that a software update is needed or that the battery is due a change.
As an update, I went out yesterday and it was still stuck in the small ring, but if I shifted down at the back while simultaneously shifting up at the front I could get into the three smallest cogs, overriding the anti cross chain built into di2.