Airlocks bubble or they don't it doesn't mean anything is wrong.
Half my beers NEVER have a bubbling airlock, but I've never had a fermentation not happen before.
Airlock bubbling and fermentation are not the same thing. You have to separate that from your mindset. Airlock bubbling can be a sign of fermentation, but not a good one, because the airlock will often blip or not blip for various other reasons...
Like yours proved, and cooper's confirmed.
So it is a tenuous connection at best.
If your airlock was bubbling and stopped---It doesn't mean fermentation has stopped.
If you airlock isn't bubbling, it doesn't mean your fermentation hasn't started....
If your airlock starts bubbling, it really doesn't matter.
If your airlock NEVER bubbles, it doesn't mean anything is wrong or right.
Your airlock is not a fermentation gauge, it is a VALVE to release excess co2. If it bubbles it is because it needs to, if it doesn't, it just means it doesn't need too...
Often an airlock will bubble if the fermenter has been disturbed in some way, like a change in temperature, change in atmospheric pressure, the cat brushing against it, opening it up to take a hydro reading, any number of things. The co2 has sat in stasis for a period of time, then it was disturbed so it is not longer at equilibrium with everything else now. And therefore it is blipping in your airlock...
Or you could indeed have fermentation happening, since maybe your fermentation was laggy and a change in temp restarted fermentation.
Airlock bubbling only tells you that co2 is coming out of the airlock, it is not telling you why. And there's various reasons. That's why it's not a good idea to equate airlock bubbling with fermentation...It could be because it is fermenting, or it could not be because of fermentation...so it's not a trustworthy tool.
And airlocks sometimes bubble or they don't. And airlock is a valve, a vent to release excess co2...NOT a fermentation gauge. It's important to make that distinction, or you'll be panicking everytime a an airlock doesn't bubble, or stops bubbling.
Fermentation is not always "dynamic," just because you don't SEE anything happening, doesn't mean that any-thing's wrong,, and also doesn't mean that the yeast are still not working diligently away, doing what they've been doing for over 4,000 years.
That's why you need to take a gravity reading to know how your fermentation is going, NOT go by airlocks, or size of krausen, or a calendar, the horoscope or the phases of the moon (those things in my mind are equally accurate).
The most important tool you can use is a hydrometer. It's the only way you will truly know when your beer is ready...airlock bubbles and other things are faulty.
The only way to truly know what is going on in your fermenter is with
your hydrometer. Like I said here in my blog, which I encourage you to read,
Think evaluation before action you sure as HELL wouldn't want a doctor to start cutting on you unless he used the proper diagnostic instuments like x-rays first, right? You wouldn't want him to just take a look in your eyes briefly and say "I'm cutting into your chest first thing in the morning." You would want them to use the right
diagnostic tools before the slice and dice, right? You'd cry malpractice, I would hope, if they didn't say they were sending you for an MRI and other things before going in....
NO fermenters are airtight, if they were then probably half our beers would end up on the ceiling. Airlocks are vents or valves, to release EXCESS co2. Many folks just cover their fermenter buckets with a piece of plexiglass letting the co2 push out between where the plexiglass and the bucket meet. Others cover their carboy mouth with tinfoil. Totally ignoring the need for either an airlock OR a bucket cover.
An airlock is a vent, a valve to release EXCESS co2, it prevents the fermenter from being airtight, and the beer from exploding all over the place.
A lot of folks, especially folks with arthritis, barely even put the lid on tight at all, they just lay it on top. again, if co2 is getting out, NOTHING nasty can get in. And that really is all that matters.
There's even a new gasket out now that renders an airlock totally unnecessary.
Your beer is cushioned by a layer of co2. And if it's getting out elsewhere nothing's getting in. The bad stuff are not ninja acrobats it doesn't take much to prevent them from getting to our beer.
And don't forget
https://www.homebrewtalk.com/f39/fermentation-can-take-24-72-hrs-show-visible-signs-43635/, and by visible signs we don't necessarily mean a bubbling airlock.
It IS a sticky at the top of the beginners forum for a reason, afterall.