Player-persistent variables reset upon leaving the End

hi everyone :D

first forum topic here.

so i'm not fully new to MCreator and this website; i've been using MCreator for almost a year now and I'm getting used to the more advanced features. but now i need some help...

in my mod (still a heavy W.I.P.), I made an item called Ender Heart, designed to increase player health on right-click. when it is used, it increases a global player-persistent variable of type integer (with initial value of 0) by 1, as long as the value is less than 4, the maximum limit of "health boost modifier" (i'm kinda bad at naming stuff :P). the variable is supposed to determine the amount of health boost you get, and the item itself is a drop from the Ender dragon. my mod adds post-Ender Dragon content as well, with even more stuff to discover in the End, only unlocked after finishing some quests & boss battles. the variable is working well (it can be changed according to my desires), except for a problem that is for some reason, once the health boost mod variable was set to 1+, it resets to 0 every time i leave the End. that's just a waste of health and time, isn't it? I'd like to know why player-persistent variables reset upon leaving the End dimension in my case, as said in the title. does anyone know whether or not this is a bug? if so, what other alternatives can be used? are NBT tags a viable option? any help would be appreciated.

thx in advance and have a good day/afternoon/evening/night.