Same for me, lack of coverage so no peak, I've never seen anything else myself.
There's an unlikely chance that it's a highly fragmented genome, see Suppl. Figure 3 in 'The Plastid Genome in Cladophorales Green Algae Is Encoded by Hairpin Chromosomes'. But again, unlikely.
I assume you did use the jellyfish tool to count the kmer? If oyu used any other software (ntCard ?) you need to modify the input count table before uploading it to genomescope
It might also depend on the kmer size you used, so try to play around with that one a bit and see if it gets better?
I removed the -C option from jellyfish and it worked thank you very much jellyfish count -m 17 -s 1000000000 -t 10 /home/vshare/bowtie2/trimmed.fastq -o reads2.jf