If you're receiving the message below (or similar), the issue is most likely related to the version of the extension you are using:
"The Bananatag extension for Gmail was unable to detect the email body."
This may be due to a conflict with another browser extension. Initially, you should try refreshing your browser. If the error is persistent, the extension will be automatically disabled.
You can re-enable the extension in the top Bananatag menu under Extension Status.”
Once the new version is loaded, if you refresh Gmail, you should see the extension load and be able to track, schedule and snooze emails as usual: