Master slide layer pausing when loading

Hi Articulate community, I'm hoping you might be able to help - it's a little confusing so I'll try and explain as best as I can.

I have a master slide set up with a layer on it, which I have created a countdown timer on. It counts down by reducing 'second' and 'minutes' variables each time the layer ends (which is 1 second long).

This is great until I create a slide with this master slide as its master, and put a layer on this new slide. This causes the master slide's layer (and therefore countdown timer) to stop.

I can't share the actual doc as it's work IP, but does anyone have any idea on how I can fix this, and make the master countdown timer work on all slide's layers?

Thanks