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.
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.
Fermentation is not always "dynamic," just because you don't SEE anything happening, doesn't mean that anything's wrong, and also doesn't mean that the yeast are still not working dilligantly away, doing what they've been doing for over 4,000 years....
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....
It's the same with your beer, if one person reports that for whatever reason they didn't get an blip in the airlock, YET they had a beautiful fermentation, then it pretty much proves that airlocks are a faulty indicator. In an ideal world they bubble...but that is often not the case, so instead somethig more reliable like a hydometer is a better idea.
In your case since it's a lager, and you are I am assuming fermetning relatively cool, it is pretty common to have little airlock activity because the co2 is sitting even heavier on the beer, and not needing to offgas.