Visitor and Vendor names render as rectangles

I've just gone back to playing Planet Coaster (PC, via Steam), and I've noticed that some of my visitors and vendors have names which render as little vertical boxes. This is what I see for my Loony Bloons vendor, for example:

As you can see in the top bar, the vendor's name is rendered as four little rectangles for each first and last names.

I also see this on occasion with visitors. The number of rectangles isn't consistent, as if they represent actual letters in names that just aren't rendering correctly. I'm uncertain if this vendor ever had a "normal" name, or if he was created like this when I placed his shop.

Here's an example with visitors. The selected visitor has the funky "rectangles" in their name; their companion is named "zsr716720" which is ... equally suspect.

What is causing this? Am I missing a font or something? It doesn't seem to affect game functionality as far as I can tell.

The one theory I had was that the game would place the avatars of other users and have them visit the part -- this would explain the "zsr" visitor, if that happened to be a username of another user. (Planet Zoo, from the same publisher, has a similar mechanic.) This wouldn't explain the vendors, though.