Any clue what caused these or an easy way to rid of them? or at least avoid this in the future

[Moffex (demonlegs)]

I have no idea what I did with the terrain tool that caused these

[Hazelfluff]

Messed around too much I guess. Since we don’t know what caused them we don’t really know how to stop them from happening but you could select them with the select tool and then delete them that way

[Musketfall]

This issue is quite common and you’ve added terrain without turning snapping on; I’d be a bit more careful next time to avoid issues such as these. I’d recommend doing as Hazelfluff is to select them and delete them