My initial thought is that, now your base is larger the purge is possibly spawning underneath the ice. The bottom of the lake is accessible, so the npcs probably just float underwater.
Also, the area you built on is capable of spawning Level 4-5 purges. The fact that your purges are restricted may be contributing to it.
Building a second smaller location, and filling it with small placeables (pots/pans). Is the only work around I could think of.
I think they are still trying to rework the Purge system, as it does have issues.
https://forums.funcom.com/t/purges-where-are-the-fixes/45535/11