I'd stay pretty far away from that one.
The PacHy always runs off the battery first. If you're accelerating hard, the gas engine will kick in. There's no normal operating condition where the battery will display 100% charged and 0 range.
A 2018 has been on the dealer lot for at least 10-11 months, and possibly almost two years. With 40 of the 56 miles put on today, you know it wasn't driven more than once or twice in that time. That probably means both batteries (the 12V and the high-voltage) have been sitting unmaintained that entire time. That's really bad for them, and might easily explain what you experienced. With the HV battery being such a critical component, I'd not want to buy that van.
When I was shopping back in March, that's a good part of why I stopped looking at 2018s. Dealers just don't properly care for them--they're not accustomed to doing it and probably don't give it a second thought.
It's not good for any car to sit that long. Bad for the tires, fluids, oil, gas... Nothing good happens when a vehicle sits idle for a long time.
2019 Pacifica Hybrid Limited