I have PDF containing a grid, which I merge with a blank page. (The PDF was exported from PowerPoint.) However, the lines in the grid do not get faithfully reproduced. Instead, the lines get shifted over and down. See the following screenshot, with the original at 25% opacity and the output at 100% opacity:

Environment

Which environment were you using when you encountered the problem?

$ python -m platform
macOS-12.5.1-arm64-arm-64bit

$ python -c "import PyPDF2;print(PyPDF2.__version__)"
2.10.3

Code + PDF

This is a minimal, complete example that shows the issue:

from PyPDF2 import PdfReader, PdfWriter, PageObject

reader = PdfReader('./grid.pdf')
writer = PdfWriter()

page = reader.pages[0]
mediabox = page.mediabox
blank_page = PageObject.create_blank_page(None, mediabox.width, mediabox.height)
page.merge_page(blank_page)
page.mediabox = mediabox
writer.add_page(page)
writer.add_metadata(reader.metadata)

with open('./grid-output.pdf', 'wb') as outfile:
  writer.write(outfile)

grid.pdf