Wow! What is causing these awful wrinkles in the wallpaper (Photo 1) ?!
The walls in this powder room were not perfectly plumb. This is pretty typical, and with many wallpaper patterns, not really a big deal. With this geometric pattern, however, getting a precise pattern match in the corners was important. But since the corner was crooked, manipulating the right edge of the wallpaper to butt into the corner would match the pattern perfectly, but resulted in the left edge of the wallpaper strip being warped (not straight), and this resulted in wrinkles. It also left an un-straight edge for the next strip of wallpaper to try to butt up against.
This wallpaper was very pliable, and also on a non-woven substrate, which is practicably indestructible, and so I was able to pull, push, twist, brush, squeegee, etc., until finally (15 minutes) the paper laid flat against the wall.
The paper may have been flat against the wall, but the left edge was not straight. And I had to butt another strip of wallpaper against it. If I had been hanging a number of subsequent full-length strips, it probably would not have worked. But my next strip was a sole one (ending in the corner to the left) and was only 10″ or so wide. This 10″ width was narrow enough to make it malleable, and to allow me to manipulate it to butt up with the previous piece to its right. Because it ended in the corner on the left (not pictured), its un-straight left edge didn’t matter.
Interestingly, the next day, I hung paper in another room in the same house, and ran into issues of twisting paper / unplumb corners on at least two walls.