Since the last commentary from Mark, I also thought of it being a problem with the PATH, and how it was written; so I moved the files to a directory in my root folder.
I did another test just to be sure, my PATH is as follows:
/Users/roberto/temp/test.dwg (Title block)
/Users/roberto/temp/logo.png (Image)
and the PATH of the image as reported in the Reference Manager
./logo.png

Just to make it as simple as possible, this time I didn't add any text, nor I changed the color of the stroke of the image; just attached the image, saved and tried to insert it in Fusion.

Just to reiterate, I didn't move any file since the creation of the DWG, I saved it on the directory "temp", I attached the image, I saved, and I tried to insert the DWG.
Regarding your second question, I use macOS in spanish (as it is the regional default for Mexico City) and Autocad 2015 in english. Could it be a problem with Autocad 2015? If that was the case I could just download the newest version of Autocad and install it (I have an Educator account).
Any way, I thank your response and your time in advance for reading this long explanation. I'll wait eagerly for your response.
PS: I'll repost the new file and the image, just in case it has something to do with the image that I'm using.