[One (M8) Q&A, Help & Troubleshooting] CRJ343:
I looked in the log as suggested and got the following :-

*****************

SuperSU installer

*****************

mount: losetup failed 1

cat: /fstab.*: No such file or directory

- Mounting /system, /data and rootfs

mount: '/dev/block/mmcblk0p47'->'/data': Device or resource busy

mount: '/' not in /proc/mounts

2+0 records in

2+0 records out

2 bytes transferred in 0.001 secs (2000 bytes/sec)

3+0 records in

3+0 records out

3 bytes transferred in 0.001 secs (3000 bytes/sec)

12+0 records in

12+0 records out

12 bytes transferred in 0.001 secs (12000 bytes/sec)

3+0 records in

3+0 records out

3 bytes transferred in 0.001 secs (3000 bytes/sec)

/tmp/updater[989]: /system/toolbox: not found

- Extracting files

mkdir: 'supersu': File exists

Archive: /external_sd/UPDATE-SuperSU-v2.82-20170528234214.zip

inflating: common/chromeos/kernel_data_key.vbprivk

inflating: mips/supolicy

inflating: arm/suinit

inflating: armv7/supolicy

inflating: arm/chattr.pie

inflating: arm64/suinit

inflating: common/chromeos/kernel.bootloader

inflating: x86/supolicy

inflating: arm64/libsupol.so

inflating: mips/sukernel

inflating: armv7/sukernel

inflating: common/chromeos/kernel.keyblock

inflating: mips64/libsupol.so

inflating: mips/libsupol.so

inflating: mips64/su

inflating: x86/chattr

inflating: x86/sukernel

inflating: x86/su

inflating: common/init.supersu.rc

inflating: common/99SuperSUDaemon

inflating: META-INF/MANIFEST.MF

inflating: arm64/chromeos/futility

inflating: mips64/suinit

inflating: x64/libsupol.so

inflating: META-INF/CERT.RSA

inflating: x86/chattr.pie

inflating: x86/suinit

inflating: common/Superuser.apk

inflating: common/hexpatch

inflating: META-INF/com/google/android/update-binary

inflating: x86/su.pie

inflating: common/chromeos/kernel.config

inflating: META-INF/CERT.SF

inflating: common/000000deepsleep

inflating: mips64/supolicy

inflating: x64/supolicy

inflating: arm/libsupol.so

inflating: armv7/libsupol.so

inflating: mips/su

inflating: armv7/su

inflating: common/init.supersu.rc.24

inflating: mips64/sukernel

inflating: x64/sukernel

inflating: x64/su

inflating: common/frp_install

inflating: META-INF/com/google/android/updater-script

inflating: mips/suinit

inflating: armv7/suinit

inflating: mips/chattr.pie

inflating: armv7/chattr.pie

inflating: arm/supolicy

inflating: arm/chattr

inflating: arm64/supolicy

inflating: x64/suinit

inflating: x86/libsupol.so

inflating: arm/sukernel

inflating: arm64/sukernel

inflating: arm/su

inflating: common/launch_daemonsu.sh

inflating: arm64/su

inflating: common/install-recovery.sh

inflating: common/file_contexts_image

CANNOT LINK EXECUTABLE: cannot locate symbol "__aeabi_memcpy" referenced by "/sbin/liblog_htc_sbin.so"...

page record for 0xa77a102c was not found (block_size=16)

- Detecting system compatibility

CANNOT LINK EXECUTABLE: cannot locate symbol "__aeabi_memcpy" referenced by "/sbin/liblog_htc_sbin.so"...

page record for 0xb634302c was not found (block_size=16)

- System-less mode, boot image support required

- Creating image

CANNOT LINK EXECUTABLE: cannot locate symbol "__aeabi_memcpy" referenced by "/sbin/liblog_htc_sbin.so"...

page record for 0xa752b03c was not found (block_size=16)

- Mounting image

mkdir: '/su': File exists

- Creating paths

mkdir: '/su/bin': File exists

mkdir: '/su/xbin': File exists

mkdir: '/su/lib': File exists

mkdir: '/su/etc': File exists

mkdir: '/su/su.d': File exists

- Removing old files

- Placing files

rm: /su/bin/su: No such file or directory

rm: /su/bin/daemonsu: No such file or directory

rm: /su/bin/supolicy_wrapped: No such file or directory

rm: /su/lib/libsupol.so: No such file or directory

rm: /su/bin/sukernel: No such file or directory

******************

Boot image patcher

******************

- Finding boot image

--- Boot image: /dev/block/mmcblk0p42

CANNOT LINK EXECUTABLE: cannot locate symbol "__aeabi_memcpy" referenced by "/sbin/liblog_htc_sbin.so"...

page record for 0xb10eb03c was not found (block_size=16)

- Extracting ramdisk

CANNOT LINK EXECUTABLE: cannot locate symbol "__aeabi_memcpy" referenced by "/sbin/liblog_htc_sbin.so"...

page record for 0xab02003c was not found (block_size=16)

--- Failure, aborting

I:Found no matching fstab entry for uevent device '/devices/virtual/block/loop0' - change

See losetup --help

losetup: needs 1 arg

*************************

IMPORTANT NOTICES

*************************

First reboot may take a

few minutes. It can also

loop a few times. Do not

interrupt the process!

*************************

.....any bright ideas about what went wrong here ?