This is a known single player bug, it’s been widely reported and. it’s on Trello
Single Player requires more resources in order to run the game world + the game, unlike playing on a server. However, with my PC, it runs smooth as butter since the latest patch. There are a multitude of things that can cause performance issues in single player, not everything game related.
There is nothing related to changing server settings and causing the disruption you are seeing.
Basically, 99% of the time, there isn’t a lot of difference between official server play and single player, but there are server vs single player bugs that do show up. Duplicate/triple/qudruple spawn issues being just the latest one.