I have a problem truncating the x-axis labels of highcharts. On my website, when the labels are truncated, it shows these strange characters in this image

When I use the exact same code in JSFiddle, it seems to work fine and instead of weird characters it displays ... how it should

Has anyone had the same problem? I use the same imports and the same version of jQuery in JSFiddle.
I thought this might be an encoding problem, but I use UTF-8 for encoding, as in JSFiddle.
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
Here is the JSFiddle link, I hope someone can help me.
Thanks in advance!
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