We tried to upgrade our SXA to SXA 1.9. We follow Sitecore documentation but we found some of the templates are merged incorrectly, and items created with those templates were incomplete.
We wrote to Sitecore support and we found this is an known issue.
Solution Install the SXA 1.9 package three (3) times. This will solve problems with missing fields under some templates.
Note: Before the upgrade make sure that you have a backup of your custom scaffolding actions (actions of type ExecuteScript are affected).
More information can be found here: https://support.sitecore.com/kb?id=kb_article_view&sysparm_article=KB0588338