I hope not....It's not supposed to be.
An airlock is a VENT a valve to release EXCESS co2...A "leaky lid" does the same thing. A fermenter is not an air tight environment. You can't have airtight, AND a situation where you don't have an explosion, unless you're fermenting in a conical or a keg....You NEED to release the built up pressure somehow.
Whatever means used to achieve that end is fine. The yeast don't care. In fact many folks with arthitis and other issues don't snap the lid down on their buckets anyway, and may folks just put tinfoil, plastic wrap, metal cookie sheets or even plexiglass sheets on top of the bucket instead.Some folks just use a blowoff tube exclusively. It's really not crucial to be tight.
You're making the mistake of equating airlock bubbling with "active fermentation" that's really not what they mean.
Fermentation is not always dynamic...just because you don't SEE anything happening doesn't mean that the yeast aren't happily chewing away at whatever fermentables are in there....the only way to know comes from gravity readings, and nothing else.
Your airlock is NOT a fermentation gauge, despite what instructions or other people may have said. It is a VENT, and VALVE to release EXCESS co2 as needed. The amount of bubbles have no correlation to some concrete rate of fermentation. Initially there may be lots of bubbles, because lots of co2 is being generated in the first few days of fermentation. But eventually there's going to be less EXCESS co2 being produced, that doesn't mean fermentation is done, it just means that since most of the sugars have been consumed, the yeast are farting co2 less. SO the rate may change, or it may stop completely because there's no EXCESS being produced.
That's why you need to seperate the idea of bubbling = fermentation from your mindset.
Don't stress about what an airlock does or doesn't do. The rate or lack of or whether or not it bubbles at all, or if it starts and stops has more relation to the environment the fermenter is in, rather than fermentation itself. All it is is a vent, a valve to let our excess gas, especially co2, nothing else. It's not a fermentation gauge whatsoever.
It could just as easily be bubbling or stop bubbling for that matter, due to changes in barometric pressure, temperature, or whether or not the cat or vacuum cleaner bumped into it, as it could be to because it's still fermenting.
Activity, action, bubbles, even krausen can be affected by the envoironment just as much as it being caused by the yeast...so going by that is NOT reliable.
If you want to know what's going on with your beer, then take a gravity reading. 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....
In truth the yeast RARELY fails us, though airlock OFTEN do.