What the? Variables to parsed in the URL

Hey all, we’re sending out emails with a button with URL variables.

The problem is that when I open an email that was sent to a lead, the variables are not parsed in the URL. Instead, the URL simply contains the custom fields like so email={leadfield=email}, etc.

When I test this by sending an email to myself or one of my colleagues, everything seems to work fine - the variables are parsed in the URL as intended.
Any ideas what might be wrong?

We’re running Mautic PHP Version 7.1.26
Identify visitor by tracking URL is set to YES
Disable trackable URLs is set to YES