I run a DW 9.2.6, and jump into this error while trying to add an expression rule in my content repository.
https://www.screencast.com/t/2z2bPJPozOKM
Worth to notice, I do not get this error when adding a rule to my product schema index.
This only happens on content index https://www.screencast.com/t/MTN4q2rqEE
Both in Chrome and IE11.