Alright guys, once again I found my silly mistake by myself.
The error is pretty stupid and Zac told us about it in the save() lesson, but I didn’t listen properly 😀
Basically I was saving a different HTML element for my block, in the edit() method I used an h2 for my title but later on I will save() an h3 and this was compromising the validation.
Hope this can help,
Andrea