Hello Darren,
Thank you for your message.
Could you please clarify if you're able to connect to the remote Host machine from the mobile Viewer if you have the
Enable permission-based Internet-ID access feature
disabled?
This feature allows you to restrict the use of the RU Server to specific accounts, i.e. you might create a user and allow them to use this server as an intermediary for an Internet-ID connection. However, the user must first sign-in on the server in his Viewer:

Please note, that the Viewers that are not signed in on this server will be refused to use this server as an intermediary server for Internet-ID connection and, therefore, will not be able to establish a remote connection to Host.
Unfortunately, it's not possible to sign-in to the RU Server in the mobile Viewer yet. However, the improved mobile Viewer version is currently in development. We are going to significantly improve it by implementing a full-fledged address book that can be synced with the desktop Viewer.
In addition, if you're not able to connect to the remote Host from mobile Viewer even with the feature being disabled, please double-check if you have specified the custom server address in the connection properties. In order to open the connection properties on the mobile Viewer, please tap the three dots next to the connection address and then click on the information icon:

You will be redirected to the connection properties section. Please select the
RU Server section, toggle the
Use custom ID server option and specify your custom server's address.
Hope that helps.