Hi Joel,
You are right - the issue was with our previous Composio-managed Reddit OAuth app. We sent an email update about this, and apologies if it did not reach you. Reddit began rejecting OAuth requests from that app, including token refreshes, which caused existing connections to expire and new attempts to fail with "invalid client ID."
We have added a new managed app. Please create a new Reddit Auth Config, select Composio Managed OAuth, and reconnect through it; connections tied to the previous app cannot be migrated automatically. The unauthenticated Reddit API fallback will not bypass OAuth. The new managed app has strict shared rate limits, so for production we recommend a custom Auth Config with your own Reddit-approved OAuth app when available. We are still investigating what triggered the Reddit-side restriction.