There is a known issue where the Viewport might not work in Cubit Estimating when using a secondary monitor. You can change your Primary Display to be the monitor where your Viewport is shown to resolve this.
This is more likely to occur if you are using a Dell-branded computer or a subsidiary brand like Alienware. This issue may be caused by outdated drivers or firmware.
It is highly recommended that you consider keeping your system up to date to make sure you get the most of it. Here is a link to download the Dell\Alienware updater:
Of course, if you continue to experience trouble, it is recommended that you contact the support team for further assistance.