the final length of the sequences after qiime cutadapt demux-single does not correspond to the real sequence length

Hi All,
I have an ION TORRENT data set using primers for the V4 region. I perform the demultiplexing as follows:

qiime cutadapt demux-single - i-seqs Chip_A.qza --m-barcodes-file mapping_file_ChipA_Bacteria --m-barcodes-column BarcodeSequence --p-error-rate 0 --or-per-sample-sequences A_demultiplex-seqs. qza --o-untrimmed-sequences A_untrimmed.qza
#Saved SampleData [SequencesWithQuality] to: A_demultiplex-seqs.qza
#Saved MultiplexedSingleEndBarcodeInSequence to: A_untrimmed.qza

And when I visualize the results in
qiime demux summarize --i-data A_demultiplex-seqs.qza --o-visualization A_demultiplex-seqs.qzv
Saved Visualization to: A_demultiplex-seqs.qzv

The length of the sequences would seem to be twice as long as it should be. The length of the amplicons would be approximately 280 bp, but the results show that they are 500 bp. I attached the result:
A_demultiplex-seqs.qzv (297.1 KB)

Do you know what the error could be?

The previous step that I made was:
qiime tools import --type MultiplexedSingleEndBarcodeInSequence --input-path R_2018_07_19_20_09_31.fastq.gz --output-path Chip_A.qza

Thank you very much in advance!

An off-topic reply has been merged into an existing topic: two different sequencing chip with the same barcodes, how to use Dada 2?

Please keep replies on-topic in the future.