If MC8A is different between cells within same LAC, 3 possibilities:
1/ MC8a have some problems
2/ corrupted BSC database: try changing your LAC ID to another number then back to the initial value (for all cells in the LAC)
3/ wrong CELL / BSC / LAC mapping in the MSC
4/ MSC paging method is done based on CELL LIST IDENTIFIER containing certain cells only, and not the whole LAC.
I can’t really help you more than that, you should ask help from your local ALU support.