The question describes a scenario with intermittent connectivity issues and reduced throughput over a fiber-optic link, along with a measured increase in signal loss. This indicates an issue related to the physical layer that can be attributed to attenuation. Attenuation in fiber-optic cabling can be caused by various factors such as dirty or damaged connectors, cable bends beyond the acceptable curvature, or degradation over time caused by environmental factors. In this context, dirty optical connectors are a common culprit and can be addressed by cleaning them, which is more practical than replacing long segments of cabling. Incorrect transceivers would typically cause a persistent rather than intermittent issue; temperature fluctuations are less likely to affect single-mode fiber in this way, and multimode fiber limitations do not apply to single-mode fiber.