This was happening on other 1.14 snapshots, but 19w03c is the one I was using when I wrote this.

Basically, everytime I die, all the mobs and grounded items become invisible. The mobs can still hurt me, and I can still hurt them, but it is very frustrating when I am playing survival and my spawn is right next to a cave full of hostile mobs. The way the items and mobs become un-invisible is by me dying again.