from the patch 2.5 (ps4 cause I can’t seem to find the pc version of the patch 2.5 thread / patchnotes and highlights 
) : “Purges are no longer spawning in the Southern region of the noob river. Giving them a chance, you know?”
in the section purge fixes of this thread PS4 Update 2.5.1 (02.09.2021) - The QoL and bugfixing update! - #2 by Ignasi
I’m not sure if they posted an actual map showing the zone affected , but southern means north should work , My guess is your issue is not tied to this but some other thing ( like the number of fundations or orther stuff … ) some screenshots of your buildings may help others to detect something that would cause your issue to happen ( it may also not help at all … ) but I wouldn’t stay to focused on that south of noob river situation and try to test more if I were you 