Hey so i'm unfortunately not able to get the statistic trigger to work:

[message1]
    [message1.trigger]
        name = "statistic"
        level = "300"
        priority = "9999"
        identifier = "message1"
        resource_name = "play_one_minute"

I added this as an additional visual in the commands file to see if it triggers, it doesn't

[[command]]
        literal = "say its been 300 ticks triggered from statistic trigger"
        triggers = ["statistic-message1"]

I then tried:

[message1]
    [message1.trigger]
        name = "statistic"
        level = "1"
        priority = "9999"
        identifier = "message1"
        resource_name = "mob_kills"

but that didn't work after killing a mob either.
Each time I tested these I made sure to create a new world.
These are the correct statistics names,

I've tried resource_name = "mob_kills" and resource_name = "minecraft:mob_kills" and resource_name = "minecraft.mob_kills". I made sure to reload the Music Triggers config through the in game gui before starting a new world.

fixed in 5.4