Do you see the total value for the month when just using
? If not, you need to check your data model and data (e.g. Value needs to be interpreted as number when reading in).
For your averages, try
=Sum(Value) / Count(Value )
=Count(Value) / Count(DISTINCT Monthstart(Date) )
Instead of Monthstart(Date) (which also only works when Date is interpreted as date showing a dual value with a numeric part), you can use any field that represents a unique Month & Year combination.