They must be using NMC batteries which are fairly common and are not recommended to be charged above 80% for regular driving and not left out in very hot conditions above 80% charge to prevent battery degradation. In this circumstance the batteries are kept "cool" through their onboard temperature packages.
This is a pretty serious issue given these types of batteries have the thermal runaway issues.
I like Volvo, but I can't help but think if this happened to Tesla's there would be an uproar among people.