Ephemeral Nodes are not like Unspoiled or Legendary ones, as they only show on your mini map when you are near them, like regular node.... As in they do not give you a directional indicator from anywhere in the zone like Unspoiled/Legendary, so you need to be at the general area of the spawn location to see them on your mini map.
The Ephemeral nodes will also have a special icon on your mini map, different from the regular nodes or Unspoiled node, having a couple stars around the node type icon, but not "glowing" like Unspoiled/Legendary.

They generally will spawn "in the middle" of a "triangle area" between the three sets of regular nodes in the general area, and they are linked to those nodes as explained below.
They will also disappear after you collect from them, but will reappear after you open 2 or more of the regulator nodes nearby, as long as you're in the time frame of it's spawn window.
This is why you will see gatherers hit the Ephemeral node for the collectables, fly off to 2 or 3 other regulator nodes and open then close them, and then fly back to where the Ephemeral node spawns, as that "resets" the Ephemeral node to respawn.

Finally, once their spawn timer runs out, they poof even if you have the node open, unlike Unspoiled/Legendary nodes which you can "hold open" past their timer, so make sure you have plenty of time left when working the collectable rating up, so you don't waste your GP for a poof.

This website is great for tracking the spawn windows for gathering locations:

https://garlandtools.org/bell/