My indexer is stuck on “processing” / invalid, can you fix it?

Yes. An indexer wedged on processing, or stuck invalid after indexer:reindex, usually means a fatal in a custom indexer, a corrupted changelog / _cl table, or a dead cron that never finishes the job. We find which indexer is failing and why, clear the wedge, repair the changelog, and confirm prices, stock and catalog rebuild green, then make sure cron actually runs so it stays that way. See our Magento cron & indexer bug fixing page for the deep dive.