In general, BIA will split the index according to the split size. But some indexes so far cannot be split automatically and their size is a bigger than the threshold. That's why you get the alert.
It's possible to see this alert in transaction RSDDBIAMON2:
And in transaction TREXADMIN:
rebuild, reindex, split threshold, rsddtrex_single_table_index, bwa, business warehouse accelerator , KBA , BC-TRX-BIA , TREX BI Accelerator , BW-BEX-OT , OLAP Technology , BW-BEX-OT-BIA , BW Accelerator , BC-TRX , TREX , Problem
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