I was hosting a hardcore server recently and me and friends came across this bug, if you spectate an entity and then rejoin you get revived which I expect is not the intended behavior.

I tested this in a LAN world and on a server.jar. if you host the world and open it to lan anyone who joins the lan world can revive, the host cannot revive in this way but by creating a server using the official server.jar file you can revive as you're no longer a server host.

Steps to reproduce:

1. Die
2.  Spectate a mob
3. leave the world/server
4. rejoin the world/server
5. you are alive

when hosting a server the issue is MC-227566 as force-gamemode is set to true by default.

but when running via LAN the issue persists, when hosting a singleplayer world via LAN maybe certain settings cause it to have force-gamemode set to true but from what I'm aware there is no server.properties for single player worlds so i cannot check.