Regenerative brake malfunction?

Hello again Everyone. I have a question regarding to the regenerative brake.
The story is this night i was driving home from my friends place at night only 4 km away from my home and the outside temp was +2 degrees Celsius.
Half the way is kinda going downhill so I use the normal foot brake to take the speed from 50 to 30 km/h since its not permitted to drive faster, and then suddenly when i brake i can hear the engine running at high RPM and when i keep eye on the Eco bar acceleration it shows zero regenerative charge, and the battery was only half full.
Normally i use B (engine brake) only at the steep hill, so since the engine was slowing my car so much down in speed i didn't use it.
So i drive more around in the city to let the car warm up, and it didn't help.
I experienced this for third time now in the winter time. Is this a fail in the cars system, or it can be normal behavior in special conditions ?

Its a Prius 2010 with 148.000 km on it.

thanks for any advice and help

 

Thanks for your replies

I drove again the same route last night and it didn't act like that. I think Either the battery was to cold, or it was a software glitch.
If it happens again i will post a update and take it to the dealer and see what they say, but since it is out of warranty, no matter what it will cost me $$ if they want to check or do repair.