You mind sharing on which platform you tried it and at what point of the game the error occurred?
That happens when running the game via the itch.io client (at least on Linux), which uses Electron/Chromium.
I'd encourage you to upload native builds of the game, as the HTML5 export is somewhat of a gamble currently (it works fine on Firefox, but other browsers are more troublesome).
Edit: Ah I see you did for Windows and Mac, just lacking Linux builds. Source code it will be then :)