2015 Prius ICE didn't kick on during acceleration up to 43mph... fluke?

This has happened before but at a slower speed. Today I pulled out onto the main road and car accelerated leisurely as usual. It was strangely quieter than normal though... I look at the speedo and I'm already past 15 mph and nothing. Just electric acceleration. I press the gas harder and now I'm into the PWR range (almost to the very end but not quite) and the car just continues to build speed but no ICE kick on as usual. at around 43 mph I get concerned and floor it all the way to see if the engine would kick on and finally the gas engine kicks on. It's as if the electronics of the car fell asleep. The acceleration felt labored as only the electric motor was providing power and I'm sure it's not good for the battery to put that much strain on it at those speeds. For those interested, I was in normal mode. Not EV, not ECO, not PWR. I stopped at the light then pulled off and the car took off and ice kicked on as normal (7-8 mph). The car behaved normally for the rest of my drive.

Has this happened to you before? Is this a known glitch? An "Oh yeah us prius owners experience that from time to time" scenario? I'm sure if I take it in, they won't be able to "duplicate" the problem. It's funny when I press the EV button, and I go past 8mph or so, the car beeps (excessive speed indicator) and the ICE kicks on. But here I am doing 43 mph with the pedal almost floored and no ICE.

 

The car was fairly cold. Sat about 2 hours after my commute home. Then started it to run an errand a block away (wash the car) and started it again to go home and that's when it acted funny. Battery indicator showed one bar above half way.

 

^ Interesting. So there are normal scenarios where the ICE won't kick on even up until 40+mph? That seems strange for me and quite abusive for the battery pack. But if it's within Toyota's normal parameters then I won't be too concerned.. I'll definitely keep an eye on it..