When you are at X percentage of life, the potion / phial / HS icon pops up to remind you to use it
The icons only work if they are not on cooldown and you have an object in the bags.
You can change the% of life the icon will trigger at Trigger> Trigger1 of each icon.
If you are not Kyrian, the Vial of Serenity will never skip by not having vials in the bags.