Okay, I tried to recreate this bug on my own and could not do so. So, a few questions:
1. Do you have pop-ups disabled on your browser?
2. Which browser are you using?
3. Are you playing in browser or the downloaded version?
So, the reason it's likely erroring for you is that pop ups are blocked. The program I use has the achievements come up as pop-ups, so when your browser blocks them, it will also be blocking some of the code from playing out, which then results in an error.
I've seen itch.io marking downloads so I figure there has to be some way to, but I'm not quite sure how if there is... I'm very new to uploading here, I'm sorry to say.
If unblocking pop-ups doesn't fix it, the only thing I can think of is either trying it on Dashingdon or Moody.ink, as firefox should run it fine otherwise.