To help resolve this, please make sure you are handing the sandwiches directly to Winnie the Pooh, as this specific interaction is required for the step to register properly. Here are a few additional tips that may help:
Approach Winnie the Pooh directly and interact with him to deliver the sandwiches, rather than leaving them nearby or giving them to another friend.
Make sure you have the Toasted Picnic Sandwiches available in your inventory before interacting with him.
If the counter still doesn't update, try restarting the game and attempting the interaction again.