Common debug mode issues
GTM's preview mode is supposed to help you test your tags before publishing. But the debug panel itself frequently causes problems. The Tag Assistant browser extension conflicts with other extensions. The preview mode doesn't load on sites with strict Content Security Policy headers. The debug panel shows different behaviour from the live site because it injects additional scripts. Sometimes it just doesn't connect at all.
You opened debug mode to fix a tracking problem and now you have two problems.
Why debug mode exists
Debug mode exists because GTM is complex enough that misconfiguration is common. Tags that don't fire, triggers that don't match, variables that don't resolve — these are routine issues in any non-trivial GTM setup. The debug panel is a diagnostic tool for a system that regularly needs diagnosing.
This should give you pause. If a tool needs a built-in diagnostic system for routine use, that's a sign the tool is too complex for the task.
The alternative perspective
Tagless doesn't have a debug panel because there's nothing to configure that could break. The script detects conversion points automatically. There are no triggers to mismatch, no variables to misconfigure, no container versions to conflict.
When something is simple enough that it just works, you don't need a way to figure out why it isn't working.
If your conversion tracking regularly requires debugging sessions, the problem isn't your debugging skills. The problem is your tracking tool.