Unfortunately these errors are very uncommon, and impossible to debug without actually seeing it. The problem is coming from the initialization process, which tries to de-code the search parameters on page load. I've maybe seen a similar error about 1 or 2 times before, and it was related to a 3rd party script tempering with the HTML dom nodes within the search bar.
My first suggestion would be to delete the current search instance, and make a new one, to see if the problem persists. First, try it with the default configuration, to see if it works that way. If yes, then it's almost definitely related to something else as well. If it's resolved, then it might be a yet unknown issue – maybe with character encodings or something similar.
Let me know how it goes.Best,
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