Sorry for bringing this up but it can be usefull for other people searching this.
I turned off swap (swapoff)
Then made a label for my swap partition because i gave up trying to give it an UUID.
When the label was created, the command returned the label AND an UUID
The UUID of the swap partition is still not printed out when i ls -l by-uuid
And the UUID is valid, I use it in fstab.
(ofcourse i turned swap back on
Hope this is helpfull to someone