Hi Natalia! Thanks for providing photos.
I don’t readily recognize this, but if it’s something that keep re-appearing despite removal, my suggestion is 1) stop removing it, and 2) see a RABBIT vet and have this checked. It could very well be some sort of pre-existing condition your rabbit had before you received him and is now manifesting. The negative thing about consistently removing it is, if it’s something that can spread, removing it may release toxins in or out of the area, making it worse. It could be something consistently leaking out of him that needs to be professional removed and sterilized.
Are you able to see a rabbit vet before the holidays? I think this is wise. Again, stressing it must be a rabbit vet, not a dog/cat vet.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.