Here are some tips for working with personalization. They could go to a "Troubleshooting" or "Tips" section in personalization documentation.

1) First matching variant wins. If two or more variants match the current trait rules then Magnolia serves the first variant. The position of the variant under the parent page is therefore significant. This is important to understand if you wonder why your variant is not served. Is there another matching variant higher up? Move your variant higher.

2) A page and its variants are linked via UUID. Each variant has a mgnl:variationOf property whose value is the original page UUID. The property links a variant to its origin. This is important to understand when you export variants to other Magnolia instances for testing. The page you export from and the page you import to must have the same UUID, meaning the original page must exist in the target instance. Publish or export the original page to the target environment first.

3) Pages that have variants have a special mixinType mgnl:hasVariant. You can only import variants to a page that already has variants. The variants node must exist under the target page. You cannot import a variant under a page that has no existing variants as it won't have the necessary mixinType mgnl:hasVariant.