Mirador 3 appearance

We have updated to Mirador 3 with the idea of ​​improving the configuration and customization of the download and share buttons. We are on it, but we found the problem: the first image of the items shown is very small. In fact we have to zoom in to see it. What could be happening?
https://patrimoniodigital.ucm.es/s/patrimonio/item/179657