Problem with updating an existing visual

The uploaded code of all custom visuals are saved with the report and used by the report: so uploading a new version of your visual will overwrite the old version and a save will persist this version with the report.

This works for all custom visuals, but a little bit different for the official published custom visuals in the Office Store: those are downloaded from the Power BI CDN (Content Delivery Network) and used in the report. For speed and reliability these visuals are also cached locally, so it will take some time before a new version of a visual is being used by everyone.

So as long as you are not altering a published custom visual (or reuse the GUID), you could easily update a new version of a visual by uploading the pbiviz package and save the report. Reopening should use the new visual. There could be the case that the report is using the cached version and not the 'embedded' version. Clearing the browser/desktop cache will solve the problem directly.

And as best practise: keep the visual GUID always the same and make sure that your new visual can handle the change in functionality.