This report (as others) is filtered by fiscal year only. So if you in beginning of the fiscal year (like now) - only data / chart you see is for one month (January). Remaining months (future are zero). This problem is for most period selections - future months where sales have not occurred are meaningless to show in any graph or report with zero values…
For monthly period selection - how to get sales order trend report for trailing 12 months? Is this a bug or a feature request?