As you see in the image, the E-Mail is displayed twice, if i edit it inline, it changes but as soon as I reload the website, it is doubled again. I didn’t change anything in the contacts module regarding the e-mail.
The custom code could be affecting things in other ways - anything customizing list views, or sugarFields
But this is a bug that I have seen happen in the past, and it is supposedly fixed in the newer versions.
If you can use the browser dev tools to inspect the HTML of that field and post it here, I can try finding where it is being generated, but it takes some luck for the HTML to have something distinctive in it, sometimes it’s not possible to find things like that.
Can you upgrade to the latest 7.14.x in a test environment, and see if it helps?
Or perhaps check your viewdefs files for the contacts list view, I see you have customizations there; it would be useful to know how the definition for the email field is set-up.
This probably happened during an update from an earlier version of SuiteCRM (that happened to me also).
You should look at custom/modules/Contacts/metadata/listviewdefs.php
You will most probably find something like