Hi there. The biggest problem with trying to help you out by making these work with Visio is the fact that I kinda just did this for fun, and was tired of waiting for someone else to do it.
Unfortunately, I don't have the skillset needed to create a proper stencil within Visio. I've tried, and it's cumbersome. In Illustrator I can just build the elements out manually, like switchports, and trace over product images to get sizing right. Vectorize it, and it's good to go in most applications. In Visio, I'd essentially have to create a CAD drawing, and I haven't explored simpler ways to convert my drawings over to it. I couldn't even tell you *why* some show up as black.
It seems like previous stencils all those years ago were outsourced, and that's probably why we haven't seen anything updated in a long time.
If I find the time to dedicate to it, I might be able to in the future. For now, I can only help by making clean SVGs and hope they work for your application. I'm with you, though, in hopes that I don't have to spend my free time doing this on everything we release. I haven't even had a chance to hit the backlog that I created a year ago 😞