I forgot to say that, as suggested, I've repartitioned the card with a new partition table but without result.
Moreover, according to this thread (that involves my sd card - SanDisk Ultra UHS-I) the issue seems related to data timeout:
http://forum.xda-developers.com/showpost.php?p=33165459
The proposed solutions (by maemo.org ) are the same that I've suggested in first post, but looking better I noticed that the first one is in the cssu kernel (dto=14) and not the second.
Is it possible that my sdcard has a different dto that crashes my phone?