Need HELP with Debugging - OMV couldn't boot

Hello,

I would need help debugging and I am pretty desperate/scared

For some reason my nginx crashed last night and I couldnt reach my OMV anymore (ping or SSH...). Even rebooting didnt help... I connected my monitor and unfortunately couldnt make many pictures (it was too fast...), however i could choose debian (or recovery mode) boot - but for some reason i got the attached picture when choosing normal boot.

Looks to me like my boot media (the SSD) couldnt be found (right?) - so I opened my HP Server and checked the cables (SATA and power) but couldnt find an issue. After closing it I tried another reboot... and it worked without issues ... I rebooted 3 times without any sign of problem now and am lost

Now I am totally scared what this issue was (hack?) and how I could debug it. Would anybody be so nice to assist me with debugging?

Thank you,
Linkin

I did have issues again today, this time I got the output:

Error: hd0 out of disk (grub rescue)

Rebooting didn't help but opening and checking the cables did fix it again. And I checked: my system drive only is 4 percent full...

Can anybody please assist me with finding the bug?