Yesterday i've found out that the yellow heart canister is not giving you a perma heart when equipped, might be worth looking into as i think it is disabled or simply not working. Might be something for you @LucidTheStick
did u travel between worlds when the yellow hearts didn't work properly? cause if u go say to the nether and then back to the overworld your hearts will mess up and all u need to do is grap the hearts and place them back and it will fix the health.