If you’re seeing zero opens with clicks, it's possible that some of your subscribers have blocked "open tracking" in their email app, which won't report opens. However, "click tracking" is always tracked.
Also, Gmail will truncate emails if the rendered HTML goes past 100kb. When this happens, it breaks the open rate numbers tracking in Gmail. The editor will warn you once you're near the limit. You'll also be warned once you exceed the limit. Note: the warning in the editor is just a heads up. It won't prevent you from sending.