Failed to save: Failed to CreateCacheEntry: Received non-retryable error: Failed request: (409) Conflict: cache entry with the same key, version, and scope already exists

If you think that not enough issues were processed you could try to increase the quantity related to the operations-per-run (​https://github.com/actions/stale#operations-per-run​) option which is currently set to 30