I know how the named and their rewards work, and some named also come with chests that you can get once you beat them, but I saw in regional chat someone say something about egg nodes being able to spawn instead of ancient chests? Is that actually a thing or not?

There are certain nodes on the map that are called 'egg nodes' because they sometimes they spawn a nest rather than a chest or flotsam (depending on the node)
The only one I can think of in the summerfest map that is behind a boss is the newly added one that the new hidden boss stands in front of. The hidden boss thus far seems to be a one-time fight, however, so it's a bit of a moot point.

Alright, ty.

Link: https://www.sylestia.com/forums/?thread=91795&page=1#2 Author: Scathreoite Time Posted: 8/22/2020 at 2:21 AM There are certain nodes on the map that are called 'egg nodes' because they sometimes they spawn a nest rather than a chest or flotsam (depending on the node) The only one I can think of in the summerfest map that is behind a boss is the newly added one that the new hidden boss stands in front of. The hidden boss thus far seems to be a one-time fight, however, so it's a bit of a moot point.

I think that I found an egg node on the summer fest map, but maybe it's just my luck..
It's an area right before the entrance to the cave; a pocket to the left that's given me 5+ nests so far. Again, maybe that's just me but; it seems like an egg node-

That is an egg node, right before the caves. There is another all the way down on the beach (really close to the cave one in fact) right above the cave (not cave entrance) and right on the water.

A third is all the way to the south and east on the water itself (not in the new boss area), again right above the cave. The fourth (and last I believe) is in the area of the cave accessed by water. The entrance to the water cave is not far from the third egg, and there is a dock. The last egg node is at the very bottom of that cave.

If you dont mind spoilers, this thread https://www.sylestia.com/forums/?thread=55519 has a full map of the Fest zone (minus where the new boss can be found).

I've already seen this, but thank you for the link!