After some time, around 3-4 in-game years, for some reason peeps start to become unhappy and slow down progress a lot. They say there is not enough water or food, even though there are plenty of both. I think a little info for settlement's overall conditions could help to understand why things suddenly change.

The game doesn;t explain it well (or at all), but you need to get down the research tree to "Recreation" which lets you build Local Businesses, these improve happiness for your Nuggets.

I did manage to build one or two, but it didn't help. Probably was too late.