Inventory Disappearing When Game Loads/Lags

I run a Java Realm (1.14.4) and some of my users have reported their inventory completely vanishing when the game loads/lags. Here's the details from one such user... "but one thing I found is every time my inventory vanished it's always when I do something and then I have to wait... for example going though a nether portal, dying & respawning, getting stuff from a chest etc."

Can you please help?