What causes some papers to stretch, after booking, on walls? Seams were initially aligned, and after several minutes, seams stretch and overlap. Why? And what to do?

Most wallpapers will absorb water from the paste and this causes them to grow a bit. There should be a soaking time listed on the paper instructions. If not then go with five mins. So you want to paste a length and leave it folded for five mins. Just before its ready then paste the next bit and you