I've been using this function for a date for a long time:

@EndOfMonth(@now("d",-1,month))

This month, the function is returning this error:

Invalid Pattern: Evaluation of function "@EndOfMonth(@now("d",-1,month))" failed: Year, Month, and Day parameters describe an un-representable DateTime. (Text, position 0)

@now("d",-1,month) still returns 12/17/2018 so it's definitely an issue with the end of month function.

I tried @EndOfMonth(12/17/2018,ddMMyyyy) as well as @EndOfMonth(12/17/2018). Both say "Invalid Pattern: Evaluation of function "@EndOfMonth(12/17/2018)" failed: Year, Month, and Day parameters describe an un-representable DateTime. (Text, position 0)"