Well not familiar with Huawei I think you should start with the usual checking. if the cells are of the same cluster check if IOI is on the increase with same trend. Check if the whole BSC gets effected then it might be some hardware level issue. however if these are random cells at random locations then analyse individually as mentioned below.
As to which TRX / set of hardware gets degraded for each site when the degradation occurs. Also it might be environmental issue so check if any specific band gets degraded. check if distance drops increase or RACH failures increase with the same trend.