I have just tried connecting from a Viewer on Linux Mint 19 Cinnamon to a remote Host, but couldn't reproduce the issue as the Host screen is displayed as normal. Could you please clarify the following:
1. Do you have a Monitor driver installed on a remote Host machine? If it is installed, we recommend that you uninstall it as the Monitor driver as it is only used for the blank remote screen feature. You can check if it's installed in your Windows device list and in the Host's settings as well. In order to uninstall the driver, open the Settings for Host window and navigate to the Driver tab and click Uninstall.
2. If there is no monitor driver installed on the Host machine, please try enabling the Use legacy capture mode feature. You can enable it in Settings for Host -> Other tab.
3. In addition, please double-check if you have the Blank the Host's screen checkbox selected in Connection properties -> Additional Properties on the Viewer's side.