Unable to set markers as "this journey only"

Hello everyone,

I made a little example route with number: 630511

I'm quite new to CT (website), and although I was at first able to set markers as "this journey only", that no longer seems to work for me. Whenever I create a marker (in a route that is saved & named), I can select "this journey only", but it won't let me save it - only when I set it to public or private.
Is this a bug? I tried making duplicates of my intended route, saving and reloading... it's quite strange to me. There seems to be only one way to "select" the option in a sort of glitched manner (selecting "this journey only", changing the marker icon, mashing save, clicking the "x" in the top right of the marker edit window - but this doesn't actually get saved)

Would appreciate tips or work-arounds! Ta-ra