ICE not shutting off when idling or under 44

I have a 2012 v with 195k miles on it, all recalls handled. In just the last two weeks, I've noted that the car does not always drive like a normal Prius (switching to EV when stopped or lower load/speeds etc). The car seems to drive fine for the first 20-30 minutes. But on longer 45+min trips, it stops enabling EV. So the best example of this is I'll drive from DC down I-95 for an hour or more and get off on my exit. As I'm coasting down the offramp, it keeps running. Stop at the stop sign, keeps running. Continue down the road, stop at the stop light, it keeps running. It might stop after two or three minutes. But then the second I take my foot off the brake, the ICE turns back on rather than staying on EV until the throttle increases. Also it's important to note that no, this is not because the hybrid battery is drained because of climate or extended EV driving.
I've had the same battery since I bought the car. I've had two different battery tests done (dealer and advanced Auto) and it checks out fine.
Any thoughts on the potential things I should be looking for? Should I just get rid of it? I wish I could get another 100k but it's making nervous.

 

No codes. Dealer says it's fine too. Battery is one or two bars from max which is its standard behavior.

 

Yes I've checked the battery with a voltmeter myself as well. 12.55 under no load, 12.4 with everything but the hybrid system running. Just didn't have a way to do it under load which is what I was hoping they would do.

 

Just cleaned the battery fan and duct filter. Did not seem very dirty.