ITSxpress currently only supports primer sets in the "normal" forward orientation where for ITS1, the forward primer is in the 18S and the reverse is in the 5.8S, or for ITS2 the forward primer is in the 5.8s and the reverse primer is in the 28S. Your mock data set uses the primers from Taylor et al. (2016) which are in the reverse orientation. This limitation is documented in the README section.
ITSxpress does not currently support reversed primer sets, but it is on the roadmap for the next incremental release, probably in May.