Hi Robert, so your network curve structure seems to be fine... I'm not sure exactly how you got the bottom sliced up into some little pieces but like burr mentions it's not just naked edges there are some little teeny tiny slivery surfaces in those segmented areas as well.

Check out Burr's video - the main way you would want to construct this is to select your curves, run Network, then hide or delete the curves to get them out of the way (they can interfere with edge selection later on). Then select the surface that you just created and run Construct > Planar on that, that will seal off the top and bottom planar openings and you'll have a solid, which should then be well behaved for filleting, I've attached the result here.

I guess at some point you did an operation like boolean or trim on that bottom zone which tries to intersect things and cut away material, that must have ended up slicing off some kind of degenerate slivery pieces that then got in the way after that...

- Michael