how many attempts per day ? (to ensure that the 50% HOSR is relevant)
I would assume there is :
Either, a coBCCH coBSIC in the vicinity.
Or, a clock issue in the SUM.
For the clock issue, you have to find an OSS engineer to check SUM alarms, or ask to replace the SUMA on the field.
Basically, you can only do 2 thigs :
1/ find which relations are faulty, and check the bcch/bsic usage on the map
2/ test a change of BSIC
3/ ask to troubleshoot the SUMA Clock. Ensure the SUMA synchronisation configuration is correct.