To ensure you receive push notifications from your Pass, make sure Notifications are on for both your Wallet app and your Pass.

Go to Settings > Notifications > App notifications > Google Wallet and make sure all notifications are allowed.

Google Wallet app > Select the Pass > Tap on ••• > Pass Details > Enable Get notifications for this loyalty card

When testing, try deleting + re-adding the Pass in your Google Wallet if you're noticing that you're not getting the pushes anymore.

This is due to Google throttling push delivery after 3 pushes per 24h timeframe to prevent spam.