If I'm not mistaken, the line error: disk lvmid/... says that you have an Logical Volume Manager (LVM). So, I believe that's why the grub rescue didn't recognise it, since LVM is different from standard partitioning. I'm not mastering LVM, so couldn't help much. But have you tried to mount it by using the live-boot USB? Then you may want to backup your data into external drives.
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If I'm not mistaken, the line
error: disk lvmid/...says that you have an Logical Volume Manager (LVM). So, I believe that's why the grub rescue didn't recognise it, since LVM is different from standard partitioning. I'm not mastering LVM, so couldn't help much. But have you tried to mount it by using the live-boot USB? Then you may want to backup your data into external drives.