This was reported to me by email from someone using pub.dev, so I don't have a reproducible case. I'll @ him in when I get his GitHub account and maybe he can follow up with one:

Lee notes that:

It works fine on iPhone all versions, and iPad up to 13.3, but not later.  
Share.share simply does nothing on the broken versions, it doesn't 
appear, and no errors reported in debug console.

/cc @cyanglaz @amirh for triage.