airlock bubbling, lack of airlock bubbling, stopped airlock bubbling, fast airlock bubbling, slow airlcok bubbling, heavy metal airlcok bubbling, or disco airlock bubbling really is not an indicator of what is happening to your beer, really isn't important, and it is NOT an accurate gauge of fermentation.
You see krausen, you got fermentation.....
I have 9 different fermenters and have been brewing for a few years, and OVER HALF OF MY BEERS NEVER HAVE ANY BUBBLING IN THE AIRLOCK AND THEY ALL TURN OUT FINE!
If you've oxygentated, and pitched plenty of yeast, then you SHOULD reach your yeast attenuation, and get close to the final gravity.....that is all that is important...NOT whether or not you airlock goes "blip" or "Rattattattatta!!!!"
An airlock is a vent for excess co2, nothing more, it's to keep your beer off the ceiling, and is designed to vent and still keep stuff out of your beer....that's really it...
In fact many no longer use airlocks at all, just cover the hole with a piece of tinfoil, or use a piece of plexiglass instead of a lid.
your fermentation is going nicely at it's own pace but for a dozen possible reasons your airlock isn't bubbling...simple as that. Get out of the habit of thinking it is a precision instrument and you will find you are less worried...The only precise methid of gauging fermentation is taking gravity readings.
Co2 is heavier than air...there can be plenty of co2 going on, plenty of active fermentation happenning but there is not enough excess co2 rising or venting out to actually lift the plastic bubbler
The 3 piece airlock is the most fallable of them all, often there is simply not a strong enough escape of co2 to lift the bubbler. Or they can be weighted down with co2 bubbles, or their is a leak in the grommet or the bucket seal, any number of factors.
But the good news is if the co2 is pushing out somewhere, then NOTHING is getting in.