Just noticed that virtue, being a cantrip, can be spammed and you keep getting +1 HP. It still only lasts one turn a level but someone could spam it for how many extra HP they want for a good chunk of time and for example slam into a dispensary with a ton of extra HP!
Does casting it both stack it and re-set the duration for previous castings? Because if not then having up to +10 temporary hp, taking 1 minute to cast and begining to immidiately drop at 1 hp per round, I cant see this being a problem.
Temporary HP stacks. This isn't, to my knowledge, a bug. It works for all temporary HP. Perks, spells, etc etc.
You can conceivably stack infinity. Aid stacking, Virtue stacking, Vampiric Touch stacking.
Unless it's duration is reset, then I don't think it's a problem.