Hi, thanks for your message! There's likely some script in the Gridbox theme that is interfering with the calculation of the dimensions of the hotspot SVG image (the blue circle).
If you have our PRO license, we can investigate further (as it can take some time...), otherwise, please assign some custom PNG image as your hotspot indicator in SpotEditor instead of the default SVG. Then upload the PNG image to your Joomla and enter a url of the folder where you uploaded the image in webrotate's Joomla settings under Graphics Path.
Let us know if any questions.