PICRUST error hsp.py -i KO


I’m getting an error while running PICRUST2 plugin (qiime 2018.11) that seems new (most of the posts around here dealt with the -i 16S error)
This is my command (the tree.qza file is the output of the fragment-insertion command):

qiime picrust2 custom-tree-pipeline \
  --i-table table.qza \
  --i-tree tree.qza \
  --p-threads 10 --p-hsp-method pic \
  --output-dir picrust2_results


hsp.py -i KO -t /tmp/tmpff46c3tx/placed_seqs.tre -p 10 -o /tmp/tmpff46c3tx/picrust2_out/KO_predicted -m pic

Any idea what can be the reason?

Thank you,