If you see the crossed out tracking icon :
It means that that email was sent without Docsify, and you won't get the statistics.
To avoid it for next emails:
Reload the Gmail page
Still have a problem? Open up a new browser tab and type chrome://extensionsinto the address bar to check whether Docsify is installed and enabled.
3. Still have a problem? Click on the Docsify Logo which is above Settings and enable Docsify.
4. Still have a problem? Check whether the green icon in Compose is enabled.
5. Still have a problem? Contact us on firstname.lastname@example.org