I would assume it means your file names have invalid characters in them. That's at least what I can make out from UTF-8 by looking over the topic.
Web-based (HTML) stuff is actually quite picky about how you name your files. You shouldn't use spaces or any special characters, even if your operating system doesn't forbid you using them itself.
If this is indeed the problem, the only thing you can do is go back to your files and change how they are named - which will of course cause problems as you have to re-assign all of these files in every instance within your project again. I think I've read it might be possible to export your event data into text files and change stuff like that in there. But simply importing it back obviously won't work - so there is probably a bit more to that solution.
The only other thing I could come up with is that the archiving itself causes problem. Maybe you have to change that? I guess it would be best to look up itch.io's help about html games for that: https://itch.io/docs/creators/html5
Sorry for the vague input, but maybe it'll help you out. If someone has more (better) information about that topic, feel free to jump into the conversation.