Crypted disk disappeared

Hi all.

I've an iMac 27 with Fusion drive, but my startup disk is an SSD via Thunderbolt 2.

I use the internal 1TB disk (fusion) only for files.

I've tried to crypt it today with the command via CRTL-Clic on it. macOS 10.13.x show me a window for insert password and in the end, when the process has started, the disk disappear.

After 2 hours, the disk is actually hide and it's impossibile to see it (also in Disk utility).

Anyone here can help me to understand how is the process and how much time I have to aspect for it? It seems there is no way to see a progress bar or something else.

Thank you in advance