My bike has the same issues. It behaves as if the Intuvia doesn't recognize the battery, that is, the Intuvia works the same with and without the battery. It also seemed to fail on the second use -- that is, it would work fine at home, but then when I went to return from my destination, it would fail. For example, this morning the power assist turned on okay, but after I shut down the bike (without riding it), the power assist would not turn on.
There's a couple of threads on this forum discussing the issue (e.g. "
Bosch system startup issue," in Forum> Advanced Ebike Forums> Maintenance and Repairs). I cleaned the contacts on the base of the Intuvia display (with alcohol and a cotton swab), and made sure the contacts on the back of the Intuvia display bounced back when pressed in (the contacts are spring loaded), with perhaps some improvement. I cleaned the contacts on the battery and the battery mount, with no improvement. One suggestion was to clean the +/- control, either by disassembling it or blasting it with compressed air. (I haven't tried either yet.)
I borrowed a battery and found that battery worked well, with only occasional difficulties turning the assist on. In those cases, I would remove and replace the Intuvia, and that action seemed to allow the assist to turn on. But not with the original battery -- the assist would just not ever turn back on. The original battery (and other bike firmware) was updated in January 2017. The battery firmware version is 5.20. The borrowed battery is version 4.00.
One thing I've just noticed on the failure is that the battery does not light up on those occasions when the power assist won't turn on. Also, the configuration menu won't display information about the battery.
I have found that if I turn on the battery with the battery button (with the battery in the bike), the assist will then works.