Hello, Bruce Kieffer. Thank you for using the Apple Support Communities to request help with Safari for macOS. We understand the situation and how you are noticing that a previously closed Safari tab will appear again automatically. We know that being able to manage your open tab and tab groups in Safari is a useful feature and we’re happy to help research what may be causing this.
There are several Apple Support articles that we’d like to provide you with to start. These articles explain how to use the tabs group features in Safari, and how to fully close open tabs:
Group tabs in Safari on Mac - Apple Support
Close tabs in Safari on Mac - Apple Support
If you have already been using these steps to manage your open tabs, we can help you more. To continue, it would be good to find out if this same behavior occurs while your Mac is started in safe mode. Safe mode can help isolate out the software that could be causing the tab to remain open. You can find instructions for safe mode in this next article:
Start up your Mac in safe mode - Apple Support
If you continue to notice the same problem in safe mode, it may be best to clear your Safari browsing history and website data before arranging your tabs and tab groups again. Please note that this step would permanently remove your history and other website data from Safari. You can use these instructions to clear this Safari data:
Clear your browsing history in Safari on Mac - Apple Support
We hope that these troubleshooting steps allow you to get back to using Safari as you would like. Please let us know if we can help you further with this.
Cheers!