To resolve, go to Gmail app, the Settings, the General Settings and the turn off Open Web Links in Gmail - see screenshot.
Then, ensure that SPIN Safe Browser is the default browser. Go to Android Settings, search for "default" or "browser" and find the area (it's different on different Android versions) and set SPIN to be the default browser.
Finally, ensure that Boomerang is set to "Block Browsers" so that only SPIN Safe Browser works. You can set this from Parent Mode or from the Boomerang Web Management Dashboard.