I think I know what kind of error you mean, but I've already found a workaround to it, so it doesn't bother me as much.
The one I'm talking about in this thread is completely different. It's not that I can't start smelting, it's that once started, the page keeps reloading on it's own and, for some reason, the smeltery is unable to load the time (I can only guess that these two facts are connected). In the picture below there should be the smelting countdown next to the phrase "Pozostały czas" (time remaining), but there is not.

And just to be clear, updating pretty much everything there is to be updated (OS, software and firmware) is the first thing I do when preparing a new computer.
In the browser console I'm getting these, but I'm getting them on literally every gladiatus page, so I don''t know if they're connected with the issue.
[Violation] Avoid using document.write(). https://developers.google.com/…8/removing-document-write
[Violation] Parser was blocked due to document.write(<script>)
[Violation] Parser was blocked due to document.write(<script>)
[Violation] Avoid using document.write(). https://developers.google.com/…8/removing-document-write