The permission errors you're seeing every week are due to a security policy for unverified Google Apps Script projects. When a script with broad permissions (like editing all your spreadsheets) is triggered automatically, Google forces a re-authorization after about a week to ensure a user is still in control of the app.
How to Fix It
You have two main options:
Get Your Script Verified: This is the best long-term solution. You need to publish your script as a Google Workspace Marketplace app through the Google Cloud Platform (GCP) console. Go to your script's settings, find the associated GCP project, and submit the OAuth consent screen for verification. Once approved, the permissions will no longer expire.
Use a Document-Bound Script: If the script is for personal use, link it directly to a specific Google Sheet instead of making it a standalone script. Document-bound scripts are generally more stable with triggers and might not require re-authorization as frequently, though this isn't a guaranteed fix.