PWA - tabbed windows

I was enjoying several PWAs that on installation gave me the option to enable tabbed windows. Recently, though, this option is no longer available even though I have every PWA flag enabled. I found it particularly useful for sites like Outlook.com (Mail on one tab, Calendar on another, open messages on yet others, for example) and Reddit, where posts automatically open in new tabs. Using Reddit now, clicking on a post in the post list opens a new browser instance to display the post.

I know there was a problem with tab labels overlapping, but that was a minor irritation that didn't affect functionality.

Was the experiment judged a failure, even though it worked so well in some cases? Or have I missed a setting somewhere?