In the problem fixture, while using the switch , it doesn't come on
correct ? You Have that jumper from one switch to the other correct ?
The Black on that romex should be attached to the other side of that
switch going up to the fixture . The white could be attached to the
other neutral in that box at the switches , giving a neutral to THAT
fixture . The 2 fixtures could share the same neutral . Now this would
be correct if we are understanding each other . I also hope that you
are using a tester ( other than a continuity tester ) to determine
that that neutral is indeed a neutral , and not tied in hot elsewhere .