Ok , from my re-read of your posts so far , I'm sure you've gone over all the easy stuff, so we'll have to blast , or at least take the diagnose to the next level.
You're dealing with an issue on one circuit ( fuse ) is the power wire to all the fixtures the same color ?
Can you see the wire leading to every fixture , is the furthest fixture from the fuse the end of the wire?
As you work back towards the fuse are there scotch lock connectors that hook the fixture wire to the main wire ?
Between the wire holes in the ceiling , can you move the main wire back and forth at all ?
I'll check in frequently looking for your answers to these questions , then we'll proceed.
BTW: 12 volt electrical was my specialty for 33 years , we can and will get this figured out.