Comment 3 for bug 1763641

it seems the squashfs might carry information about how it was built (flags used), so we could check them and also tell in the error that a too old snapcraft or something was used:

$ unsquashfs -s /var/lib/snapd/snaps/core_4443.snap
Found a valid SQUASHFS 4:0 superblock on /var/lib/snapd/snaps/core_4443.snap.
Creation or last append time Wed Apr 11 17:24:03 2018
Filesystem size 88629.63 Kbytes (86.55 Mbytes)
Compression xz
Block size 131072
Filesystem is exportable via NFS
Inodes are compressed
Data is compressed
Fragments are not stored
Xattrs are not stored
Duplicates are removed
Number of fragments 0
Number of inodes 12819
Number of ids 19

I didn't investigate properly but I think "Fragments are not stored" might relate to the required -no-fragments options.