My husband and I live in a 100-year old Victorian. About five years ago, we had someone hang wallpaper in the large foyer, along the hall and in the second-floor hallway. About one year later (perhaps a bit longer), the wallpaper started coming apart at the seams.
Too bad, but fixable. The hanger forgot to put glue sizing on the walls before pasting the paper. It’s always needed, even with so-called self-sizing paste. The paper is probably strippable, so pull it off the wall carefully for re-use. Wash all the paste off the walls, then apply glue sizing on them before putting up the old (or new) paper with vinyl paste.