Error on build.

Full log here:
Build (/usr/bin/uck-gui --wait-before-exit) started at 2020-03-20 18:12:12
Sorry, try again.
Sorry, try again.
>> Ubuntu Customization Kit 2.4.7 on Ubuntu 19.10, 5.3.0-42-generic x86_64
Starting CD remastering on Fri Mar 20 18:12:27 EDT 2020
Customization dir=/home/john/tmp/customization-scripts
Mounting ISO image...
mount: /home/john/tmp/remaster-iso-mount: WARNING: device write-protected, mounted read-only.
Unpacking ISO image...
Unmounting ISO image...
Mounting SquashFS image...
Unpacking SquashFS image...
Unmounting SquashFS image...
Creating apt cache...
Creating root home...
Mounting /proc
Mounting /sys
Mounting /dev/pts
Mounting /tmp
Mounting /home/john/tmp/remaster-root-home
Mounting /home/john/tmp/remaster-apt-cache
Mounting /run
Mounting /home/john/tmp/customization-scripts
Copying fstab/mtab...
cp: '/etc/mtab' and '/home/john/tmp/remaster-root/etc/mtab' are the same file
Unmounting /home/john/tmp/remaster-root/var/cache/apt...
Unmounting /home/john/tmp/remaster-root/tmp/customization-scripts...
Unmounting /home/john/tmp/remaster-root/tmp...
Unmounting /home/john/tmp/remaster-root/sys...
Unmounting /home/john/tmp/remaster-root/run...
Unmounting /home/john/tmp/remaster-root/root...
Unmounting /home/john/tmp/remaster-root/proc...
Unmounting /home/john/tmp/remaster-root/dev/pts...
Failed to copy mtab, error=1
Build ended at 2020-03-20 18:15:00
Build (/usr/bin/uck-gui --wait-before-exit) started at 2020-03-20 18:17:25
>> Ubuntu Customization Kit 2.4.7 on Ubuntu 19.10, 5.3.0-42-generic x86_64
Starting CD remastering on Fri Mar 20 18:17:32 EDT 2020
Customization dir=/home/john/tmp/customization-scripts
Removing remastering root dir...
Removing ISO remastering dir...
Mounting ISO image...
mount: /home/john/tmp/remaster-iso-mount: WARNING: device write-protected, mounted read-only.
Unpacking ISO image...
Unmounting ISO image...
Mounting SquashFS image...
Unpacking SquashFS image...
Unmounting SquashFS image...
Creating root home...
Mounting /proc
Mounting /sys
Mounting /dev/pts
Mounting /tmp
Mounting /home/john/tmp/remaster-root-home
Mounting /home/john/tmp/remaster-apt-cache
Mounting /run
Mounting /home/john/tmp/customization-scripts
Copying fstab/mtab...
cp: '/etc/mtab' and '/home/john/tmp/remaster-root/etc/mtab' are the same file
Unmounting /home/john/tmp/remaster-root/var/cache/apt...
Unmounting /home/john/tmp/remaster-root/tmp/customization-scripts...
Unmounting /home/john/tmp/remaster-root/tmp...
Unmounting /home/john/tmp/remaster-root/sys...
Unmounting /home/john/tmp/remaster-root/run...
Unmounting /home/john/tmp/remaster-root/root...
Unmounting /home/john/tmp/remaster-root/proc...
Unmounting /home/john/tmp/remaster-root/dev/pts...
Failed to copy mtab, error=1
Build ended at 2020-03-20 18:28:04
Build (/usr/bin/uck-gui --wait-before-exit) started at 2020-03-20 18:31:43
>> Ubuntu Customization Kit 2.4.7 on Ubuntu 19.10, 5.3.0-42-generic x86_64
Starting CD remastering on Fri Mar 20 18:31:51 EDT 2020
Customization dir=/home/john/tmp/customization-scripts
Removing remastering root dir...
Removing ISO remastering dir...
Mounting ISO image...
mount: /home/john/tmp/remaster-iso-mount: WARNING: device write-protected, mounted read-only.
Unpacking ISO image...
Unmounting ISO image...
Mounting SquashFS image...
Unpacking SquashFS image...
Unmounting SquashFS image...
Creating root home...
Mounting /proc
Mounting /sys
Mounting /dev/pts
Mounting /tmp
Mounting /home/john/tmp/remaster-root-home
Mounting /home/john/tmp/remaster-apt-cache
Mounting /run
Mounting /home/john/tmp/customization-scripts
Copying fstab/mtab...
cp: '/etc/mtab' and '/home/john/tmp/remaster-root/etc/mtab' are the same file
Unmounting /home/john/tmp/remaster-root/var/cache/apt...
Unmounting /home/john/tmp/remaster-root/tmp/customization-scripts...
Unmounting /home/john/tmp/remaster-root/tmp...
Unmounting /home/john/tmp/remaster-root/sys...
Unmounting /home/john/tmp/remaster-root/run...
Unmounting /home/john/tmp/remaster-root/root...
Unmounting /home/john/tmp/remaster-root/proc...
Unmounting /home/john/tmp/remaster-root/dev/pts...
Failed to copy mtab, error=1