Well. I change my stance. It appears Sol's burst effect not applying was not the issue, but apparently the update broke all forms of elemental resist. I've noticed Reiki's fire resist doesn't apply as well, so I would assume it to be the same for a lot of other similar skills (Gaia's thunder res, Kyuki etc). That 6 hour maintenance wasn't perfect lol.
Edit: Also, paging Slashley, although don't mind me if it's pointless, but A Sol's heal buff (well, buffs. She casts 2 of those) gives a 50% heal boost, which I also confirmed in the DMM wiki. Each buff should theoretically give 25% heal, although I'd need to come across an enemy that cleanses buffs to confirm.