Firestore onSnapShot: can't unsubscribe

[nmandyam]

I have an onSnapShot listener on a collection with a where clause - nothing unusual. I'm trying to stop the listener from kicking in when I move from one page to another. I do that by invoking the function that's returned when I set up the snapshot, as described in the doc. But the snapshot continued to kick in regardless, even after I invoke that function. I don't even know how I'd track down the issue. All help appreciated!