If you see that combo of expired and received transaction regularly, it means your wallet is "behind" the mint with the value of recovery index used to generate ecash. Head to Settings > Recovery > Increase indexes to fix it.

It's true that to claim received zaps you need to open the app - Minibits ecash lives in your device, it's not server-side custodial solution.

Minibits uses background processing (even when app is killed) via encrypted push messages to receive nwc commands to send zaps. There are however issues that android tend to interrupt such processing in some cases, so until this can be made more resilient I won't increase the scope of bg processing.