You are bumping up against the 10000 bot limit. Each cycle, the program kills off bots to keep the population at or below 10000. Actually, it doesn't kill them, it re-uses their slots in the bot array, effectively killing them. You don't see the actual sim population hit 10000 because births are handled before deaths in the cycle and some bots die nautrally each cycle, dropping the population at the end of the cycle to something less than 10000. It's the high water mark mid cycle that isn't allowed to go above 10k.
The super long ties only last a cycle. The program still draws them even though the slot a tied bot is using gets re-used for a different bot. They all end up going to the same bot, the one that is occupying position 10000 in the rob array (I think).
So, technically, it's a bug. I should probably formally kill bots (and their ties) according to some human defined policy (oldest, weakest, etc.) when the population exceeds 10k, but today it's essentially random death. The logic to detect overly long ties and delete them kicks in the following cycle, which is why the ties dissappear after a cycle. I've not fixed this to date since few peopel run sims this populous and also, its a simple visual way to know your sim is clipping.
