yes, you need microscope to thoroughly check, especially for dusty and damaged connectors(scratched), i recommend cleaning ends with proper methods,
also if there is light coming out any other part of the wire, or loss of light at the end, that is sign of crack, also if that is the case an Fiber Optic Light meter or else a VFL i think, will let you know
this stuff is very delicate, and easy to break in your fingers, as we found out when we troubleshot
( i cannot go in to detail about your systems, i was only trained to support the wire)