Unknown skip operator 'victim_explain'

 Unknown skip operator '' for field 'victim_explain'., referer: https://e.h.org/interface/patient_file/summary/demographics.php?set_pid=71728

The victim_explain is a part of the history form. I know that the skip operators are in the options.inc file. I can’t grasp what the error message is suggesting

v6.1.0
ubuntu 18.x
Apache 2.4.x