when entering the nether, I can hear mobs attacking me while still on the loading screen. when I finally loaded in I was missing a few hearts.

in one instance I heard a ghast shoot me and the portal broke while on the loading screen, after I finally loaded in the portal was broken and it created a new portal right in front of it.

in another instance I was just loading into my world and on the loading screen I heard a witch attacking me, and the second the game loaded I died.