Thank you for clarification.
Please, do the following:
1. Fully exit the Viewer (File -> Exit).
2. Locate the file config_4.xml in the Remote Utilities Viewer %appdata% folder.
3. Remove the config_4.xml file from that folder.
This will reset the Viewer settings/options. Your address books won't be affected by this action.
After performing the above steps, please update Host and Viewer to the latest version. You can download it on this page: https://www.remoteutilities.com/download/
Please note, that version mismatch between Viewer and Host/Agent may lead to performance issues and some features not working. Also, if you use the self-hosted server (RU Server), please update it to the most recent version too.
Let us know if the problem persists.