(Please ignore the post) Calc Mgr error validating @ISMBR function

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Hi,

Just in a sudden, a business rule that previously validated and deployed successfully now got failed on validation the @ISMBR function. So, in the business rule there is conditional check IF(@ISMBR(@LIST("A","B","C"))) which has no issues at least before this week, today when validate the same rule without any changes, it failed saying something about optimizing formula failed which seems weird to me and don't make sense. Even I tried update it to be IF(@ISMBR("A","B","C")) also failed with same message. From the error message, it seems now @ISMBR only support the parameter to be single member only rather than either single