When running a function that contains /say commands, the order of execution is incorrect - specifically, commands involving /say 

To reproduce:

Start a new world, with a datapack that contains this function:

say a
tellraw @s "a"
say b
tellraw @s "b"
say c
tellraw @s "c"

Run this function, you will get these results:

a
b
c
Executed 6 command(s) from function 'foo:bar'
[Player] a
[Player] b
[Player] c

You would expect to get:

[Player] a
a
[Player] b
b
[Player] c
c
Executed 6 command(s) from function 'foo:bar'