It's multiple past loops (hundreds of them) and only Ivovnne remembers because of her brainwashing power/the Mirror of Truth. Initially, Winter's spell was to return to the past but it became a timeloop that wouldn't stop until Penelope (the only one with some semblance of immunity to Ivonne's brainwashing power as the last ancester of the Ancient Mages) would manage to stop Ivonne or until her soul would completely shatter.
Unfortunately, it took hundreds timeloops for Penelope to get here because she was under the curse that made everyone hate and Ancient Mages (that curse comes from the Lailas).

Current Winter forgot (until the recent chapters) but his body and soul didn't, which is why his body temperature is unaturally warm since he's being consumed with flames as a punishment for that taboo spell.