My indexer is stuck on "processing" or shows "invalid", can you fix it?
Yes. We run bin/magento indexer:status to see which indexer is frozen, commonly Product Price, Catalog Search or Stock. A status stuck on processing normally means a reindex was killed and never reset, or a lock is held. We reset the indexer state, run indexer:reset if needed, then a clean indexer:reindex, and confirm every row reports Ready.