Got it! 
The problem was that the /etc/openswap.conf file is empty and hence the encrypted swap partition canât be found.
It should look similar to this:
$ cat /etc/openswap.conf
## cryptsetup open $swap_device $crypt_swap_name
# cryptsetup open $swap_device $crypt_swap_name
## get uuid using e.g. lsblk -f
swap_device=/dev/disk/by-uuid/49c1c4bd-924a-4d1a-ac71-20374181d8de
crypt_swap_name=luks-49c1c4bd-924a-4d1a-ac71-20374181d8de
## one can optionally provide a keyfile device and path on this device
## to the keyfile
keyfile_device=/dev/mapper/luks-9380def9-db67-404c-99f2-3583072f3b58
keyfile_filename=crypto_keyfile.bin
## additional arguments are given to mount for keyfile_device
## has to start with --options (if so desired)
#keyfile_device_mount_options="--options=subvol=__active/__"
## additional arguments are given to cryptsetup
## --allow-discards options is desired in case swap is on SSD partition
cryptsetup_options="--type luks"
Note: The keyfile_device is the root device ( / ).
Hi @Fabby , I couldnât find how to inform the development team. I think they should be informed, because this bug is in the ISOs version 21.2.4 and 21.2.5 minimal and effects every boot not only resume.