The mean link is probably the “path balance”.
It shows the difference between UL path loss and DL path loss.
If value = 0, then it is perfect.
If value is above +8dB or below -8dB (approx), then it proves that the cell is suffering from HW issues in UL Reception or in DL Transmission path (from antenna to TRX and vice versa).
HW failures in one direction will badly impact all KPIs related to that cell.