You most likely have to re-install KPVBooklet, I don't think it is bridged across updates.
Note: fw-5.9.x changes the schema of the database files used, which might effect KPVbooklet.
Whereas an fw update does not change the portion of storage where the user databases are kept, do to the changes in database structure - 5.9.x is an exception to the general rule.
Unlike some other models, I do not recall seeing any reports related to the PW2 model having been posted.
On the other hand, problems related to firmware version 5.9.x have been reported.
Have you look into the KOReader forum here for any mention of firmware version related problems?
https://www.mobileread.com/forums/fo...play.php?f=276
(I don't use it so I don't follow it.)
A helpful answer? I must be mellowing with age.