a. Reindex from Magento admin *sometimes not all indexers are reindexed using admin reindex > check also reindex via SSH
Go to System > Index Management and check indexers status
Select the items that are marked as "Reindex required" and go to Actions > Update on schedule
This will trigger a reindex for selected indexers.
Important: Sometimes not all indexers are reindexed using admin reindex even if time & date is showing as updated in magento admin. We recommend to double check the reindex process using the SSH/CLI reindex method presented below.
Reindex mode: You can set your indexers as "Update on Save" and store entities will be indexed when saving admin configurations or as "Update by Schedule" and indexers will be reindexed recurrently (default once / day) . In order for "Update by Schedule" to work ok, make sure your cron jobs are running correctly on your server. Your hosting partner or development team can help you with the cron jobs configuration.
Resourse from reindex information