Sync Rate: d6016.0/u512.0 kbps RCO: d84.0/u64.0% Noise Margin: d9.0/u16.0 dB Power: d7.0/u12.0 dB Attenuation: d6.0/u2.0 dB (Approx. Distance: 0.43~0.44km)
How, exactly, do those line stats look good? The line is at 84% RCO on the downlink! At that level, I would expect to see the sync dropping regularly.
Based on the reported Attenuation (short distance), it seems the line card isn't putting out enough power for a stable connection. Ask the line card owner to increase the power till you get a more reasonable RCO on the downlink.