Did you change the tab name using tab settings?, here are steps I would follow to troubleshoot
- Check the limitations first https://docs.microsoft.com/en-us/power-bi/collaborate-share/service-embed-report-microsoft-teams#kno...
Known issues and limitations
- In Microsoft Teams, when you export data from a visual in a Power BI report, it's automatically saved to your Downloads folder. It's an Excel file called "data (n).xlsx" where n is the number of times you've exported data to the same folder.
- You can't embed Power BI dashboards in the Power BI tab for Microsoft Teams.
- URL filters aren't supported with the Power BI tab for Microsoft Teams.
- In national clouds, the Power BI tab isn't available. An older version might be available that doesn't support the new workspace experience or reports in Power BI apps.
- After you save the tab, you don't change the tab name through the tab settings. Use the Rename option to change it.
- See the Known issues and limitations section of the "Collaborate in Microsoft Teams" article for other issues.
- Make sure you have not moved the report from its current location , remove and attach the report agian and see if that works
- Make sure you have access to workspace (if its hosted on some other workspace other than "My Workspace"
- I am assuming you are the original owner, if not, it's possible that the original owner has not granted you the view access
