dvam wroteP.S. the definition of the swap file in fstab has not been changed
So there is a swap definition, you should have the root definition as:
UUID=...... ext4 / .... 0 1
UUID= .... swap swap ..... 0 0
If so, genfstab created the /etc/fstab based on the existence of a swap partition during installation.
Did it exist then and does not exist now? Swap can also be a file within root ... but obarun doesn't do this.
If you can copy here what your fstab looks like it would help to figure this out.
% sudo blkid | grep swap
will also show if there is a swap partition on the disk and what its uuid or /dev/ id is.