I'm on season 2 with the Sawyer filters and I'll recommend 1. using the bleach solution and drying the cartridge as best you can before storing it for the winter and 2. backflushing and testing flow at the season's start.

I took the gravity system on a hike in May and it took a day to get the flow above a trickle, when normal is nearly a liter a minute. I'd done everything except bleach treatment before storing and clearly it had clogged with bacteria &/or mold (no smell, so I'm guessing bacteria).

I'd also do the bleach treatment after any trip filtering obviously stagnant water.

FWIW the backflush faucet adapter works much better than the syringe that ships with the Squeeze. I can't get that to stay on.

Cheers,