This is fixed in April 2018 (released one years ago):
Large bookmark file sizes caused performance degrade Jira issue ID: OP-4261 Large bookmark files caused performance degrades. QlikView documents took a long time to open or close. Starting from this version, Qlik NPrinting removes temporary bookmarks from the file. In case of navigator crashes, the InfoText part is compressed, and there is a limitation to a maximum of 256 bookmarks.
So the solution is to upgrade the installation to April 2018 or a newer version (now February 2019).
Best Regards, Ruggero --------------------------------------------- When applicable please mark the appropriate replies as CORRECT. This will help community members and Qlik Employees know which discussions have already been addressed and have a possible known solution. Please mark threads with a LIKE if the provided solution is helpful to the problem, but does not necessarily solve the indicated problem. You can mark multiple threads with LIKEs if you feel additional info is useful to others.
Further to Ruggero's comment, I suggest upgrading specifically to NP Feb. 2019 SR 1 or later versions to leverage many bug fixes and performance enhancements. See the accompanying NPrinting Product release notes for each version of NPrinting to view corresponding bug fixes, performance enhancement and limitations.
Please remember hit the 'Like' button and make helpful answers as 'Solution Accepted'... Cheers!