Strange broken link in HTML

I have set a new Mailwizz instance for one of my client and see a strange issue. Whenever I send a campaign, the HTML code of campaign contain a broken link on domain
something like :
<img src=3D"" height=3D"2" w=
idth=3D"3" alt=3D""></body>

I double checked number of times before sending and there was no such link but when I get the campaign and check HTML code I see this link. Any clues what is wrong ?

Mail-tester deducts .5 points for this broken link with this error :
[404 - Error : Not found]