Uploading mod creates blank workshop item?

I’ve tried uploading two different mods now, and both of them create blank 0.000 MB workshop items.

I’m following the tutorials to the best of my ability, the item seems to hang at 25%, where the program claims I have unsaved changes and asks if I wish to discard them.

What the workshop looks like

the warning I get

Founded in 2004, Leakfree.org became one of the first online communities dedicated to Valve’s Source engine development. It is more famously known for the formation of Black Mesa: Source under the 'Leakfree Modification Team' handle in September 2004.