Hi @DCristino
this problem generally arises when the image is removed or moved from the Onedrive /Drive/Dropbox directory
or when security permissions are changed or updated and tightened and you cannot longer access to the image externally. This is very probable specially if you say that everyone in the team experienced the same issue.
You can try updating the photo again, take the public URL of the photo
and replace the link in the HTML of your signature.
Hope this helps