Little update: after everything I couldn't access the two disks as shares from Windows. I tried to connect to data1_1 and I was forbidden to access it.
Connecting via ssh I noticed that data2_2 was in /mnt but not in /share/1000, and, as suggested, I deleted data1_1 before rebooting.
I manually recreated data1_1 and data2_1 in /share/1000, chmod-ed them to 777 (like the others), rebooted the nas, but still I cannot access them...
I set a protected share where my user is allowed to access with full permissions, but it seems it doesn't work...