Thanks, nice to know what exactly caused it.
The game uses SharedArrayBuffers (to allow for multithreading). Itch warns pretty clearly in the project page that their implementation for it is experimental, and it shows. I don't really mind, as long as the second-project-download-link works.
I tried adding multiple files or pay-what-you-want, but never both together. I'll give that a try once I add the Linux version and see whether it works.