This problem has been recognised for some years in the US (written up very nicely by Tom Moloughney in the BMWBLOG - https://www.bmwblog.com/2017/04/17/bmw-address-issue-incorrect-state-charge-readings-i3/) . It has also been recently reported in this forum (2014 REx not working when battery is...
I have experienced exactly this problem with my 2015 i3 REx. I have given dealers and BMW Australia the link to the American BMW Blog, but they say that this information "does not apply" to the Australian i3 RExs. The latest suggested "fix" from my local dealer is to replace the pressure...