Combine tracks no longer an option

When I import audio books from CDs, I combine all the tracks on the CD into one for a number of reasons. I put the disk in, stop the import, select all the tracks, select the "combine tracks" option from the options menu and then click "Import CD". I have done this numberous times successfully until the latest import.

This approach worked fine for the first eight discs but on the ninth, the combine tracks menu item was not there. I tried a music CD and got the same result. I quit and restarted iTunes - same result. I restarted the computer - same result. I put in a CD that I had previously combined tracks and imported. I selected all the tracks and the un-combine option was available under the options menu. I un-combined the tracks and then tried to combine them again, but the combine tracks option was not there.

iTnues 11.1.3

Any ideas or solutions would be appreciated.