Hi @Luca_Lattarini ,
Are the number of customer ID crossing the uniques exceeded limit? In that case, it will be counted as 1 item. Also, please note that the function uses the HyperLogLog (HLL) method of approximating distinct counts. It is configured to guarantee the value is within 5% of the actual value 95% of the time. So, it's not 100% accurate always.
Thanks!