OK, all three partitions checked, only the data partition had a minor error:
check file system on /dev/sdb3 for errors and (if possible) fix them 00:00:08 ( SUCCESS )
fsck.fat -a -w -v '/dev/sdb3' 00:00:08 ( SUCCESS )
fsck.fat 4.1 (2017-01-24)
Checking we can access the last sector of the filesystem
0x41: Dirty bit is set. Fs was not properly unmounted and some data may be corrupt.
Automatically removing dirty bit.
Boot sector contents:
System ID "mkdosfs"
Media byte 0xf8 (hard disk)
512 bytes per logical sector
4096 bytes per cluster
6 reserved sectors
First FAT starts at byte 3072 (sector 6)
2 FATs, 32 bit entries
3317248 bytes per FAT (= 6479 sectors)
Root directory start at cluster 2 (arbitrary size)
Data area starts at byte 6637568 (sector 12964)
829227 data clusters (3396513792 bytes)
16 sectors/track, 4 heads
0 hidden sectors
6646782 sectors total
Reclaiming unconnected clusters.
Checking free cluster summary.
Performing changes.
/dev/sdb3: 7022 files, 169348/829227 clusters
Returned card to Kobo, still no change.
