Since the Prime also has a chunk of the battery dedicated to hybrid driving it's pretty easy to dip into that reserve causing it to take a little longer to charge back to full. I do it often if I find myself in the EV zone of the throttle as I drive down the road my house is on. It's not uncommon I'll park with only a sliver of the hybrid battery reserve left but before the ICE kicks on to recharge it. When recharging the traction battery it'll have to cover that too which could account for 20-30min. Just running the remote climate prep has it tell me it needs 20 more minutes to finish charging because it goes pretty slow when it's close to 100%, even on a level 2 charger