Hello @fdoctor,
I have solved this problem in my another thread dedicated to differnt bug (ITS extraction error - Missing sequence for record beginning on line 17 - #11 by salias) and I got rid of your problem by removing all older versions of ITSexpress (I suppose, maybe conflicting???) and I reinstalled ITSexpress on ver. 2.1.1. (lately 2.1.3.) in environment qiime2-amplicon-2023.9. Good luck 
Karel