Intermitent bug on encrypted swap over Ubuntu 18

Wanting encrypt swap and the only script I found to do it as I want is it:

    sudo -i     cd /root      mkdir -p ./.myfolder      cd ./.myfolder      swapsize='4G'      curdir=$  (pwd)      flNmDev="myfile"     flPtDev="$  curdir/$  flNmDev"      flNmKey="mykeyfile"      flPtKey="$  curdir/$  flNmKey"      flNmMnt="mydevname"      flPtMnt="$  curdir/$  flNmMnt"      fallocate -l $  swapsize $  flPtDev &> /dev/null     chmod 0600 $  flPtDev     chown root $  flPtDev      dd if=/dev/urandom of=$  flPtKey bs=4096 count=1 conv=notrunc,noerror &> /dev/null      sudo chmod 0600 $  flPtKey     chown root $  flPtKey cat << EOF > /etc/crypttab # <target name> <source device>         <key file>      <options> $  flNmMnt $  flPtDev $  flPtKey swap,offset=1024,cipher=aes-xts-plain64 EOF     cryptdisks_start $  flNmMnt &> /dev/null     mappedCryptPath="/dev/mapper/$  flNmMnt"     mkswap -L swapone $  mappedCryptPath -f &> /dev/null     rpl "/swap.img" "#/swap.img" /etc/fstab &> /dev/null     echo "$  mappedCryptPath none swap sw 0 0" >> /etc/fstab     swapon -a  

On the same machine and same Version of Ubuntu it sometimes works but sometimes crash on boot.
Following some output on each boot it did:

uname -v  #54-Ubuntu SMP Mon May 6 18:46:08 UTC 2019 

journalctl -b   systemd[1]: Mounting /boot... swapon[995]: swapon: /dev/mapper/mydevname: swapon failed: Device or resource busy mkswap[991]: mkswap: unable to erase bootbits sectors  systemd[1]: systemd-cryptsetup@mydevname.service: Control process exited, code=exited status=1  systemd[1]: systemd-cryptsetup@mydevname.service: Failed with result 'exit-code'.  systemd[1]: Failed to start Cryptography Setup for mydevname.  systemd[1]: Dependency failed for Local Encrypted Volumes.  systemd[1]: cryptsetup.target: Job cryptsetup.target/start failed with result 'dependency'.  systemd[1]: dev-mapper-mydevname.swap: Swap process exited, code=exited status=255  systemd[1]: dev-mapper-mydevname.swap: Failed with result 'exit-code'.  systemd[1]: Failed to activate swap /dev/mapper/mydevname.  systemd[1]: Dependency failed for Swap.  systemd[1]: swap.target: Job swap.target/start failed with result 'dependency'. 

cat /proc/meminfo | grep Sw  SwapCached:            0 kB SwapTotal:             0 kB SwapFree:              0 kB 

cat /proc/swaps   Filename                Type        Size    Used    Priority 

cat /proc/swaps   Filename                Type        Size    Used    Priority /dev/dm-1                               partition   4193788 72704   -2 

cat /proc/meminfo | grep Sw  SwapCached:        10644 kB SwapTotal:       4193788 kB SwapFree:        4102396 kB 

journalctl -b  mkswap[868]: mkswap: /dev/mapper/mydevname: warning: wiping old swap signature. systemd[1]: Found device /dev/mapper/mydevname. systemd[1]: Activating swap /dev/mapper/mydevname... mkswap[868]: Setting up swapspace version 1, size = 4 GiB (4294438912 bytes) mkswap[868]: no label, UUID=348deb8f-7457-4829-a1a2-0ebd1b61f6d6 systemd[1]: Started Cryptography Setup for mydevname. systemd[1]: Reached target Local Encrypted Volumes. kernel: Adding 4193788k swap on /dev/mapper/mydevname.  Priority:-2 extents:1 across:4193788k FS systemd[1]: Activated swap /dev/mapper/mydevname. systemd[1]: Reached target Swap. 

cat /proc/swaps   Filename                Type        Size    Used    Priority /dev/dm-1                               partition   4193788 0   -2 

journalctl -b  mkswap[683]: mkswap: unable to erase bootbits sectors systemd[1]: systemd-cryptsetup@mydevname.service: Control process exited, code=exited status=1 systemd[1]: systemd-cryptsetup@mydevname.service: Failed with result 'exit-code'. systemd[1]: Failed to start Cryptography Setup for mydevname. systemd[1]: Dependency failed for Local Encrypted Volumes. systemd[1]: cryptsetup.target: Job cryptsetup.target/start failed with result 'dependency'. systemd[1]: Dependency failed for dev-mapper-mydevname.device. systemd[1]: Dependency failed for /dev/mapper/mydevname. systemd[1]: Dependency failed for Swap. systemd[1]: swap.target: Job swap.target/start failed with result 'dependency'. systemd[1]: dev-mapper-mydevname.swap: Job dev-mapper-mydevname.swap/start failed with result 'dependency'. systemd[1]: dev-mapper-mydevname.device: Job dev-mapper-mydevname.device/start failed with result 'dependency'. systemd[1]: Activating swap /dev/mapper/mydevname... systemd[1]: Starting Cryptography Setup for mydevname... systemd-cryptsetup[688]: Volume mydevname already active. kernel: Adding 4193788k swap on /dev/mapper/mydevname.  Priority:-2 extents:1 across:4193788k FS systemd[1]: Activated swap /dev/mapper/mydevname. mkswap[690]: mkswap: error: /dev/mapper/mydevname is mounted; will not make swapspace systemd[1]: systemd-cryptsetup@mydevname.service: Control process exited, code=exited status=1 systemd[1]: systemd-cryptsetup@mydevname.service: Failed with result 'exit-code'. systemd[1]: Failed to start Cryptography Setup for mydevname. 

cat /proc/meminfo | grep Sw  SwapCached:            0 kB SwapTotal:       4193788 kB SwapFree:        4193788 kB