kmer missing

[Dkaaaaa]

Dear fellows,

There are some special symbols (defined by me) in my sequence, then I used the software for kmer generation and found that the number of kmer generated is not correct, I checked the generated kmer file and found that there are no kmer with the special symbols defined by me, is there any way to avoid this, attached is my sequence, very much looking forward to your reply!

Belows are my code :
jellyfish count -m 21 -s 100M -t 48 -o result.hash target_transcript.txt
jellyfish dump -c -t -o kmers.txt result.hash

target_transcript.txt