Disaster / Destruction
When you're so xenophobic that you get xenophobic towards yourself... yeah then it might be time to stop being so xenophobic. Well, the Old Ones didn't and they had a giant civil war over it but hey, that's just the way the stagnant xenophobia goes.
Well, a more extreme version of the already extreme xenophobia rolled in like it had any business there among the original Old One subspecies, which made up the largest portion of Old One society, of maintaining the Old One genome. This is well and good until it happens that some of the DNA from regular Old Ones isn't present in the GMO versions, with the new ones being about as genetically similar to regular Old Ones as chimpanzees are to humans - which, according to these regular Old One extremists, isn't enough similarity to be allowed to live. These extremists, who also happened to be in charge of the government, wanted to wipe out these GMOs and replace them with new ones that possessed the full Old One genome, with the genetic differences that allow them to survive being present in additional DNA.This led to civil war. Something about the GMOs not wanting to die. Anyways, many of the more populous types of GMO took this stance as well against both regular Old Ones and other GMOs, resulting in a many-sided war. At the same time, an alien empire rose to try and attack them while they were fighting among themselves but this was wiped out by being attacked by the regular Old Ones. The forces that had to be sent to deal with this empire resulted in many of the super-weapons not being well enough defended and so some of them were stolen by the rebel groups. This led to super-weapons being used against all the factions and this included the release of many GMO diseases that were able to spread through portals and also led to the creation of automated "hunter ships" that would target all but 1 species of Old One. Due to this war, the species of Old Ones basically wiped themselves out with disease, lasers, dropping meteors on their own planets (yes, really), and creating multiple genocidal robot rebellions. The worst thing was probably the fact that every planet within and near their territory was left completely uninhabitable due to scorched earth methods and most of their terraforming machines were destroyed. A few of them survived and went into cryo-sleep aboard space ships to either find habitable planets or with the hope of waiting out the war and xenophobia. The majority of these were destroyed by those "hunter ships" and the fleets of all sides passing by and noticing them - as well as the basics like being hit by meteor storms and solar flares. The inhabitants aboard often died when stored food was consumed at a faster rate than it could be recycled or by using up too much energy to try and find habitable planets - but the Old Ones had left almost no planets within the near parts of the galaxy habitable due to their genocidal behaviour towards outside life and their war among themselves.