You could try editing your Portal.bat in your SourceUnpack file. Just rightclick the file and select "Edit in Notepad". Where it says "start" copy/paste:

hl2.exe -game portal -novid -console -fullscreen -high

Then save Portal.bat and double-click the file to open the game. In the game go to "Options" then "Video" and change the Resolution to whatever is needed, click on "OK" and the game should change resolution without any errors.

Note: When using Fullscreen, LiveSplit won't show on top and you can't see your Splits because of it.

Hope I could help you.

The reason for it not being documented is it's extreme unlikelyness of happening. I think.

@DysseAlex thank you so much. I will use the Discord next time!

where did you get version 4104 from?

What about the demorecording?