There is Bug 22822649 - BI_CONTENT_AUTHOR ROLE NOT WORKING REPORT HAVING FORECAST() which is raised already for this issue.

Please help !!!

I have same problem, would you try increase the month range with at least 5 years data. One of my case is only have 4 years history data, then forecast function give me all zeros, however when I given more years data , it seem worked. I don't known the reason.

Would you able to set filter using month variable? the month column not set to prompted , set it to using presentation variable with correct operator through "Add More Options"

for Bug22855455 what is work around. please many thanks.