"SQLSTATE: Serialization failure: 1213 Deadlock found"
This error can occur during reindexing.
Category Products index is locked by another reindex process. Skipping. Product Categories indexer process unknown error: SQLSTATE: Serialization failure: 1213 Deadlock found when trying to get lock; try restarting transaction, query was: DELETE FROM catalog_category_product WHERE (category_id = ('1050'))
Either another reindex is running, or someone cancelled a previous reindex (in which case indexing for that table will remain locked).
php bin/magento indexer:reset
php bin/magento indexer:reindex