Searching Pdf in Ibooks not working

I have an iPad Pro. After updating to the latest software edition 11.2.6. The search function in iBook crashes on several of my Pdfs. I tried the restart mentioned in an earlier post from last year with no effect. There are some pdfs that it works on just fine but two larger ones (500+ pgs) it will shut down iBooks. I have no problem searching the same Pdfs on my HP laptop nor do I have any problem if I open the Pdf in acrobat on my ipad. It is only in iBooks that the search does not work on these files. Has Apple set a limit on pdf size for searching?