gtm.js / Tag Manager outputs code upon link click

Once clicked on any link (preferrably one that doesn’t lead to another page, like call-link in header menu oder “Problem melden” link above footer) gtm.js creates output href="tel: at the very end of the HTML document. (verify on any page of provided domain)

Possible origin of this output coming from this part in gtm.js:

{
                "function": "__html",
                "metadata": ["map"],
                "unlimited": true,
                "vtp_html": "href=\u0026quot;tel:",
                "vtp_supportDocumentWrite": false,
                "vtp_enableIframeMode": false,
                "vtp_enableEditJsMacroBehavior": false,
                "tag_id": 7
}

This is surely not the expected behaviour. What’s going on?

Cheers

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