It's something to do with the splicing in of new paper rolls during the printing process.
I'll confess that I don't fully understand how it all works, but am confident I've tracked down something very close to what you found.
Splice rupture tabs
These tabs are die cut and/or perforated to break instantly after the splice has been made to release
the new roll for unwinding. They are also used to hold down the outer spire during rotation to prevent air pockets being formed (which can burst the splice preparation during acceleration). The number and type of tabs are determined by splice speed, paper grade and pattern shape.
I don't quite follow how they would end up at the orientation shown in your image, but it is certain that they should not make it through to a product for sale, those pages should have been counted as wastage.
You can read more in the PDF I used as a source which might, or might not, help you to a fuller understanding!.
Edit: A further PDF seems to confirm that these are ‘Splice rupture tabs’ which are used to hold a roll of paper closed prior to it being spliced to the preceding roll.
The tabs are rectangular and have adhesive on the underside at both ends but not the centre where there is a die cut line or perforation. The ungummed portion goes over the edge of the roll.
Double sided splicing tape is attached further back from the leading edge than the rupture tabs.
The splicing machinery, I think, picks up the new roll by pressing the double sided tape onto the roll that is finishing, and cutting that roll behind the join. The pick up applies tension to the paper on the new roll, rupturing the tabs and allowing the paper to feed into the press.
I can somehow understand this without being able to picture it, so I hope it makes sense to others!