I have looked at the page source, at first sight I would say that one major issue is that the jQuery script is included 3 times.
The first one in the header is the correct one, as it's enqueued by WordPress, but there are two more instances within the middle of the page (on line 375 and 379 on the main page source). I have copied that section here, see lines 1 and 5, both loading jQuery 2nd. and 3rd. times:
I would suggest removing those first, and making sure that any custom script is enqueued properly.
This may not be the exact cause though, but it's worth fixing first.Best,
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