If you find issues in this add-in, please report them at product@1990quebec.com.
The stopwatch may fail to load during presentation mode, showing an unclickable popup like this:
This occurs when the add-in is inserted directly into a presentation without being installed to your Microsoft account. You can check this by going to Insert → Get Add-ins → My Add-ins. If the stopwatch is missing from this list, it won't work in presentation mode:
Install the add-in to your account from the Microsoft AppSource page (may require admin permissions). Once installed, the stopwatch will appear in your My Add-ins list and work correctly in presentation mode: