I updated my 515 to 3.34 a few days ago - no problem.
Today it started turning itself off after a few seconds. It is fully charged, it has been reset, all pairing has been forgotten. The sequence is as follows:
1. press button to turn on.
2. Get purple flashing light (if paried or not) for a few seconds.
3. The either - green flashing light for a second or might get a second of flashing blue - then it turns off.
if I jump in whilst it is on I can change light mode. I can also connect (if quick enough) with the varia app on the phone and even re-pair it - it still turns off after a few seconds.
Any ideas, it's 14 months old.
I have raised a ticket with Gramin, but that will probably take about 5 days to answer and not sure of their response.