Just got a response from them:
I double checked the page, as mentioned before the page has a script file that overrides jQuery’s browser object which is defined in jQuery migrate and Master Slider JS file.
In order to isolate and find the issue, please try to deactivate all plugins on your website.
If that resolved the issue, reactive each plugin individually until finding the cause.
This isn’t to do with the theme – so can you please try this?
– Ed