In 3.2.0, the maximum setting for numeric digits is 16. If it is set higher when one of the math functions is called than error 40.1, external routine failed is raised.

So, this is working as designed in 3.2.0. This is documented in rxmath.pdf:

RxMath is a Rexx utility package that enables you to use enhanced mathematical functions.

The function names in the Rexx Mathematical Functions package are similar to the names of their corresponding mathematical functions.

The precision of calculation depends on:

• The value specified when the command is issued

• The numeric digits settings of the calling Rexx activity

Note: Precision is limited to 16 digits.

Although, one could make the argument that to truely understand that statement, one needs to look in the code.