The Poetic Edda is from the 13th century, some 200 years after most of the north converted to Christianity. There's plenty of examples where Christianity might potentially have influenced the Poetic Edda - for example it seems like strange coincidence that the first humans Ask and Embla have names quite closely resembling Adam and Eve.
In Völuspá from the Poetic Edda, Ragnarök is described in great detail. Supposedly the origin of it is a völva (seer) named Heiðr who supposedly foretells the end of the world while visiting Odin.
Was this völva Heiðr and the story of Ragnarök actually part of the Norse mythology at the time when it was a religion? It seems strange to me that the prophesied death of all prominent Gods worshiped would be part of any religion. Is Heiðr part of the mythology or is this all rather a separate, potentially newer story? The völva herself does not appear in any other myth(?) and isn't a prominent figure, unlike most other characters who tend to frequently re-appear.
There seems to be historical artifacts representing Odin getting devoured by Fenrir and the like, but these may be dated to Christian time. And it seems the death of the old Gods would be all too convenient to suit the Christian missionaries' narrative.