
This is the link. Btw, the language used is Spanish. https://worldmangas.com/news/1b82f55620779cbbd4949bdb0e524b6b/cascade

I'm sorry. I didn't notice that the link that I copied was not working.
https://lectortmo.com/library/manhwa/32780/hosigi-iyagi

imma apply my knowledge of korean dramas and documentaries to this. but i won't guarantee everything I'm gonna explain since it may not be accurate.
as we see the timelines of the side story 10 (where hosik died) to special story 8 are VERY DIFFERENT. side story 10 most probably occurred during the joseon dynasty (1300s - 1910) while special story 8 mentioned north korea. this hints at the korean war around the 1950s. or it could also refer to 1945 when the korean peninsula divided (north & south).
my guess is that the seungyeon in special chapter 8 is his reincarnation since he shouldn't look that young if we consider the timelines. he has memories of hosik who died years before. the real hosik most likely hasn't reincarnated yet. or if he did, they just haven't met yet.
anyway, the note at the end of the chapter says there will be 5 more chapters (?) after special story 8 so we'll get more information then.
I checked the raws and used Google translate. But as much as I can comprehend, seungyeon's amnesia was real.(/TДT)/
He even lied to hosik about remembering him and the kids so that hoshik wont be worried (but don't worry he will remember all the memories a month after).
Another warning after the amnesia part, we have another chapter of seungyeon from the past (or maybe a reincarnation before the present seungyeon) . I think the chapter shows how he missed hosik from the past that he even started to hallucinate of seeing him. ╥﹏╥