Recently got the same problem here, the issue was i got disconnected while opening the upgrade tabs for an azerite gear, and when i log on again, i discovered that my heart of azeroth was missing. Then i realized that i could redo the Dying World quest, and so i took the quest only to realize later that i can't continue. the quest got stuck when you are asked to speak with Magni outside of The Chamber of Heart. after all this, i just realized that the heart was placed by the game inside my mailbox saying problem with equiping/storing item. and so i took the heart right? but now im stuck with it and can't to do anything with it lol
NOTE : the screenshot here are taken after i took the Heart of Azeroth
