I've used an inline table to establish an "original" sort order, then assigned this in the properties tab.
Sample inline: List the values of the field in the order you want them to be sorted (where I have value 1, value 2.....)
Load * Inline [
Then, go into your Chart properties, in the "Sort" tab and check box "Load Order" , and select "Original" from drop-down.
You need to use real date-fields like month(date) which returned a dual-field with a string-interpretation like 'oct' for the current month and 10 as numeric value - and this could be sorted numeric in each object.
In general should be all date-fields dual and/or as doubled fields (string + numeric) - it avoids many problems by matching and calculating data against periods if you have numeric fields for them. I think this would be very helpful for you: How to use - Master-Calendar and Date-Values