Erika, Laszlo:
Thank you for your help, and apologies for not responding sooner (sidetracked by looming deadlines, as usual).
I checked wall intersections, zone boundaries, and used the copy/paste technique into another file. The problem reoccurred. Then I tried eliminating superfluous elements in the test file. No change. Then I deleted and recreated the Zone, and after utilizing the Interior Wizard again, the missing wall panels finally appeared. I'm not fully sure why it finally worked, but I could copy/paste the missing panels back into the regular file. All is well.
Thank you again.
AC27 USA/Build 5030 16" MBP