Would there be any reason where a smart publish does not make an update but a republish does?
Issue
I recently updated my Sitecore 9.2 site. We have 2 production sites. 1 on, 1 off for switch overs. Each pointing to different databases. After updating the B (Off) site, turning it on, using Sidekick (migration tool) to make sure all items are the same as develop's admin panel, I noticed some things were not working on the B site.
Although the items (in sitecore admin panel) were the same from develop -> B site, on the actual site, they were not working. Then when trying to do a Smart publish, no items were updated, but the republish updated 2 items, for this particular issue and resolved this issue. I'm worried that there are still not working even though the items are synched properly.
Speculation
Could the issue be after sidekick migration, rebuilding the db and reindexing were not done?