After an update of Windows 10 on a Dual boot system, my second disc was unrecognised by File Manager. Partitions can be seen on Gparted, but am unable to access the files on them. When I tried to mount the partitions, got the above message for /dev/sdb2

sudo fdisk -l gives:

Disk /dev/loop0: 147.3 MiB, 154406912 bytes, 301576 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop1: 194.9 MiB, 204382208 bytes, 399184 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop2: 89.5 MiB, 93835264 bytes, 183272 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop3: 91.1 MiB, 95494144 bytes, 186512 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop4: 99.1 MiB, 103931904 bytes, 202992 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/sda: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x7ebdaaa6

Device Boot Start End Sectors Size Id Type
/dev/sda1 * 2048 1952560940 1952558893 931.1G 7 HPFS/NTFS/exFAT
/dev/sda2 1952561152 1953519615 958464 468M 27 Hidden NTFS WinRE


Disk /dev/sdb: 465.8 GiB, 500107862016 bytes, 976773168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xae9ad835

Device Boot Start End Sectors Size Id Type
/dev/sdb1 * 2048 1026047 1024000 500M 7 HPFS/NTFS/exFAT
/dev/sdb2 1028094 976771071 975742978 465.3G 5 Extended
/dev/sdb5 1028096 976771071 975742976 465.3G 83 Linux

And what are the /dev/loop listings?

/dev/sdb2 is an extended partition. This means that it doesn't contain any data, only the sda5 partition. If you mount that one, it should work.

The /dev/loop mounts are files that have been mounted as partitions. I have no idea what they are, but cdrom and dvdrom images are often mounted in this way.

Given Ubuntu base, the loops are probably snaps - try "df -hT".