Using a function file I tried to call "loot give @s loot <loot table> which gave me an invisible item that took up a slot in my inventory. I tried executing the same function file over and over with no results. My inventory updated once I called the loot table myself ingame and gave me every item that I had called each time.

Strangely it doesn't update if my inventory changes in any other way (eg, calling a different loot table, even manually), and the space in my inventory will still be taken up

This may be related to MC-197349