When you run a Late Swap build on SaberSim, we will completely rebuild your lineups around the players that have already been locked into those lineups. And you can get very different looking lineups after the build. And this is mostly because of the sim precision slider. The sim precision slider is going to select a different random set of simulations to use to rebuild each lineup the same way it does when building new lineups pre-lock. Especially early in the slate or for lineups that still have a lot of players left to play and are therefore, "swappable" this can significantly change the lineup construction.
In general, this is a good thing. News breaking can change the context of a slate pretty significantly. And we want to maximize our edge by reacting to this new news as much as possible in our lineups. However, if you want to lessen the impact of Late Swap on your overall lineup portfolio, we recommend either using Quick Swap instead to make changes. Or using the toggle in the Late Swap menu under the Contest tab to only swap lineups containing out players. This will, exactly as it says, instead of swap all lineups only rebuild your lineups that already have a player that's out in them.
One final option, if you want to lower the impact of the reshuffling that you get when you run a Late Swap build is to simply turn your sim precision slider down a bit for your Late Swap builds. If you're interested in any other parts of the lineup building process on SaberSim, check out some of the other videos in our support documentation. In the meantime, thanks and good luck.