Commands do not seem to be running in the order specified in the functions and are arbitrarily ran. 

Steps to reproduce:

1. Download the Commands Out Of Order datapack
2. Drag the zipped datapack into your datapacks folder of your world
3. Set up a multiplayer game (tested in LAN)
4. Have two people connect and then run the /reload command from chat
5. Let each player kill the other for a while
6. Be sure to have both players kill each other, not just one account killing the other.

You should be able to notice how the death/kill messages are mixed and not in the same order.

execute if score @s mg.deaths matches 1 run function mglib:entity/player/main/death 

execute if score @s mg.respawn matches 1.. run function mglib:entity/player/main/spawn_split_1

execute if score @s mg.mkills matches 1 run function mglib:entity/player/main/mob_kill

execute if score @s mg.pkills matches 1 run function mglib:entity/player/main/player_kill

This is the player tick function: the death message should appear before the kill message does.