It's hard to tell what's going on for sure, but if there's a slight bulge in the center and you use subdivision with one central pole, you can get subdivision artifacts like that, you can try to use multiple loops and make sure the middle circle is completely flat or use a geo/cube sphere for a starting point and avoid…
You're SURE those verts are welded? The issue on the left looks like unwelded verts and the one on the right looks like your cage wasn't pushed out quite far enough to encompass the high poly entirely. But, of course, I could be wrong. And likely am...
With a mesh like this, you should be able to get away with no hard edges, and less uv seams really. What are you baking in? I feel like that might be the source of your problems.
btw, this is probably just camera clipping or some aliasing but to me it looks like its due to the hard edges. you getting incorrect shading on the out edges on both of the hard edge models areas in red should be like areas in green
Well how do you want it to look in the end? With the low's geo as is the result will look like a decal. If you want it to look like it's really going inwards you'll need to have the low poly geo reflect that. Normal maps are always more successful the less work they have to do.