EDIT-2: The final solution was to add this to "My Filters":

@@||lemmy.fmhy.net^$3p

Based on Adblock Plus filters explained: Exception rules

EDIT: I went to the logger and found that EasyPrivacy filter list had a specific filter for ||fmhy.net^$3p:

This is the first time I see uBlock Origin blocking images from a random domain and I don't know how to whitelist them without disabling uBlock Origin for the whole site.

Any clues are welcome!
Thanks.