
Random thoughts...I
The first emperor was yooshin's twin and was killed by YD so his longevity has nothing to do with Dojin's.
As it stands right now, Yellow Dragon is dying because his dragon pearl energy source was destroyed and he's been consuming his own power to turn back time for Dojin. I seem to remember it had been 150 years since yooguk had a new emperor when D#27 got there. (Somehow, the old and dying Dojin in oyr reality had a pearl like object he tried to hand him before that bird bastard got in the way in a dream a few chapters ago.)
Dojin #27 is definitely a peculiarity, first he was not meant to be emperor, the cat spirit switched places with him, then he showed up three days earlier than expected (not to mention his dream changed after the energy exchange with YD) ...an earlier incarnation turned the god's black scales into yellow/golden scales--probably thru the power of love, kindness and gentleness which is why YD is my cinroll seme--cause he reflects that back on his bae. Third, Dojin#27 is the first incarnation to ask/learn about the others and take measures to protect himself better as well as take on the burden of protecting Yooguk, but more than that...these last two incarnations have been encouraging YD to be free. #26 told him to dream for himself. #27 snuck him outside the fortress to see how his people lived and also asked him to come back to his reality and stay with him.
It surprises me how lax they are in dealing with the assassination attempts on Dojin, it isn't like they don't know who is behind it. Why was that one guy not put down? Seriously just bc YD can delay Dojin's death here doesn't mean they shouldn't take steps to prevent that.
It is a crazy coincidence that the bird guy committed suicide over losing Dojin in their reality and ends up an emperor in Bukro. I read another spoiler that the tortoise god had a female emperor he loved so it sucks she got replaced with that rapist jerk. And is he realky a tortoise? What happened to the other great snake who was supposed to be a god? YD's original snake form gobbled up yooshin while that other snake slept? Sh!t there are so many plotholes in this story, I understand why so many people are confused.

Agree about the first emperor (family, too fresh and attached still).
Yeah, that entire pearl thing totally blew right by me, so I didn't take it into consideration when writing the above.
Also even though Dojin's memories were erased, the last two times he has been sent back he broke his usual ending in his world and never married which I think he had done several times before.
I don't get the lack of security. If anything, that's the one weakness to the story. Even if they had been betrayed before and YD couldn't trust anyone around Dojin, he could have had their surroundings protected. Also, the animal spirits. I get he was there earlier than expected but it has been 27 times, you think that their guard would be up more than anyone else's (except YD).
On Suhoon (Crazy bird guy) this is why I thought he would play a bigger role in this because it felt like this was something that YD would have known about. Maybe he did and that's why he looks like he feels guilty when Dojin tells him that he knows he would never hurt him or that he is always kind.
I thought Suhoon was there as some sort of manifestation of YD gone wrong or some mistake on his part because it doesn't seem possible that YD would be able to watch that happen to Dojin over and over again. Maybe, in a way, that's what caused Dojin to be more active in his own protection and in helping YD.
I guess the role he played was just finishing off Black Tortoise. Chapter 58, shows the Black Tortoise still in front of the God he was praying to on 57 and it shows the loss of his empress and how deeply he loved her. But Suhoon also appears to reject him and it looks like he cut his wrist and that drives him over the edge (I don't read Korean but it seems like it is going that way). You get another image of him seeing YD and Dojin hugging and looking at each other lovingly and he decides to take YD's emperor away.
Bird boy isn't shown after that so I don't know what happened to him.
Like you said, there are quite a few plot holes here and I don't think this is the type on manga that ties up all loose ends when it concludes. I think some of the plot holes may be accidental, lost in translation or just dead ends.

The other snake is in fact the Red Lotus lady who is the "witch" in the story and is trying her best to sacrifice Dojin, so that Yellow Dragon and him are both replaced and instead she becomes the God of Yooguk along with that nasty minister as the emperor. YD original snake had actually deceived Red Lotus to become God himself and gobble up Yooshin, the prince to become the God.
These are just some questions on my part...
Spoilers of current story might be included...
Ok.
I have been wondering if Dojin holds the key to stop the cycle of loss that Yellow Dragon and Dojin have been going through.
Now, I have no way of knowing if this is the case since Yellow Dragon and Dojin have gone through this 27 times.
Initially, I wondered why the Dragon wouldn't tell Dojin what was to come so he would keep his guard up, why the Spirit Animals or extra precautions weren't taken around Dojin since assassination attempts were be inevitable.
Dojin seems to be the oddity here since it looks like the other emperors before him lasted longer. The first emperor, the twin that got his older brother to be the sacrifice instead of him, looked like he reached adulthood (so he lasted a few years at least). While Dojin, seems to be given very little time with Yellow Dragon.
The story feels like they are heading towards a tragedy because we are getting Yellow Dragon's goodbye to Dojin. He is sure this is the end of him and therefore his time with Dojin so he wants to get all the time he can with the man he loves.
Dojin, on the other hand, is kept (or least he tries to keep) worried free and unaware of the times he came back, their previous history and the dangers that surround him. The way Dojin takes those cakes from hot guy (whose name slips from my mind) freshly after coming back from near death after his wine was poisoned was crazy to me since he is aware that this happened (he didn't die, Yellow Dragon, sent him back in time that's why the number of death is still 27, I think).
Yellow Dragon may have tried this before (preparing Dojin for the worst) and it didn't work out. Or he has lost him so quickly after getting him back that he can only think about spending more time with Dojin.
But the story that we are getting now is Yellow Dragon being resigned to losing Dojin forever. It is like he has tried everything and nothing has worked and now he knows he is out of power and that means that if he goes, so does the opportunity of being with Dojin.
But I don't know.
I don't think it will be a tragedy.
I think something about Dojin is not meant to be in that world. They get all these people from Dojin's world who may or may not die young but who aren't held back by their deities.
I know Yellow Dragon is different and more powerful than the others. But Dojin is also special above all the other emperor's in Yellow Dragon's life. He changed him to Yellow Dragon (his scales were that of the black snake before Dojin) and he was the only one that was kind and broke through YD's detached nature. The only one that YD loved.
But I think that what might not have been tried before is Yellow Dragon dying in his world, and that perhaps that would allow him to be reborn in Dojin's.
As I said, this is all speculation on my part, and questions I have been asking throughout the story.
P.S.
Also, I had thought that that rapist SOB would play a bigger part in all of this and for now, he appears to have fizzled out. Just like that he lost interest in Dojin. Maybe he just affected the Tortoise and that was it but I really expected him to have bigger role.
Instead, it just seems like no matter what, Dojin is not supposed to be there because every effort to protect him is always met with failure. The spirit animals knew the urgency of being around Dojin but kept being held back and this time around even got murdered which I assume has to be a huge no no in that world.