This is a common result for especially old or especially soiled books. The streaks themselves may contain some ImmacuClean, but usually do not.
Typically the streaks contain leftover soil and paper fines (by microscopic and FTIR inspection).
Following the Imcuclean instructions, you should allow the book to dry once then wipe it again with DI water, and then allow it to dry a second time before pressing. This will eliminate any streaks. Try to wipe orthogonal to the streaks that you see on the book itself. allow to dry and repeat if necessary

Here’s a link to the immacuclean instructions for use, which may help

immacuclean instructions jan 2022