«وَإِنْ كَانَ الْحَدِيثُ فِي نَفْسِهِ مَشْهُورًا»
Even if the hadith itself is widely transmitted.
This establishes that mashhur and fard nisbi are not inherently contradictory labels. They assess different aspects of a transmission history: mashhur describes the overall spread of a report, while relative singularity identifies an isolated link in relation to a particular teacher or narrator.
Overall pattern: a report has three or more sufficiently distinct paths after a Companion.
Particular pattern: one teacher occurring within those paths is represented by just a single transmitting student.
Therefore, hearing that a report is “mashhur” does not exclude singularity in an individual branch of its isnad. Each label must be assessed at its proper level.