What is your tablet's native screen resolution?
To further analyze this issue, please download the spacedesk diagnostic script here, then extract it.
Inside you will find spacedeskDiagnosticTool.cmd, just right-click it then run as administrator (please restart first your primary machine so the spacedeskService is not hanging).
This script will start a debug view app to capture spacedesk debug traces.
On step 5 it will prompt you to reproduce the issue (by trying to connect the viewer app and let it fail), make sure to do this before pressing any key to continue.
After the script is done, a folder will be created on the same folder as the script file which contains various log files that we need for analysis.
Please right-click it -> Send to -> Compressed (zipped) folder, then attach the *.zip file on your next reply.
Looking forward to your feedback.