Huh, I've noticed Aura of Protection vanishing and needing to be manually reapplied a couple of times. I think this is when Wyll (who I have multiclassed as a paladin) has died.
I can see for him, the Aura of Protection tooltip says it gives +5 to saving throws, which fits his 20 CHA. BUT now I look more closely at the character sheet, while I can see that the +5 is mentioned in the individual Saving Throw tooltips, it doesn't seem to be actually added to the total given. For example, if I hover over Wyll's CON saving throw bonus on his character sheet, it says he has +3, but then the breakdown is +2 from CON, +1 from a ring and +5 from Aura of Protection. At the very least it looks as though the tooltip needs a bit of rework.
I'll now keep an eye out to see whether the bonus is actually being applied when there's a saving throw in the game.