Image not showing on email clients

Image not showing on email clients

Hello, recently we have noticed that some of our banners are not showing properly on certain email clients.
We have noticed that also a "hidden" class has been added as well as a "display:none!important" attribute has been added.
We don't know where it comes from.
Grateful if you could look into the matter.
Any advice/suggestions is the most welcome.
Kind regards
JM