@fortunato I forgot to say that this error doesn't show up when creating a new topic and sometimes it works also in replies. The error in the NodeBB UI is the following: "stream ended unexpectedly"
On the admin panel, the picture scales to the right dimensions except when youre in the main page, the image doesn not scale but rather zooms in.
Try changing the image class setting to cover. That should give a better result also using an image that is too large isn't really a good idea, I think the ideal size was 400x250.
@baris Ah that fixed it as long as its not too large. Thanks for the tip!