If I look at files in the vsearch /tmp/itsxpress dir there are sequences for both .r1, and .r2 , but the command executed was for single-end reads:
extract ITS2 seqs - this fails
!qiime itsxpress trim-single
--i-per-sample-sequences bastrop-sx2-outputs/sx2.demux.qza
--p-region ITS2
--p-taxa F
--o-trimmed bastrop-sx2-outputs/sx2.demux.ITS2.qza
/tmp/itsxpress dir
ls -l /tmp/itsxpress_fp0p5hbq/
total 6872
-rw-r--r-- 1 qiime2 qiime2 0 Mar 19 16:18 rep.fa
-rw-r--r-- 1 qiime2 qiime2 20 Mar 19 16:18 seq.fq.gz
-rw-r--r-- 1 qiime2 qiime2 3524967 Mar 19 16:18 seq_r1.fq.gz
-rw-r--r-- 1 qiime2 qiime2 3502500 Mar 19 16:18 seq_r2.fq.gz
-rw-r--r-- 1 qiime2 qiime2 0 Mar 19 16:18 uc.txt