Is the Year 2020 missing only in one module or the entire model?. If it is missing in the entire model then most likely your Time Settings have changed and your future year might be showing as 0 instead of 1.
But if it is missing in only one module then it can be Hide/Show. Right Click on the module and click Show all.
@Misbah I changed the time range and increased number of periods to 2 . Then i got the year 2020 in DAT03 historic volumes. After that my DEM03 Demand Forecast module gets the values for year 2020 and not for 2021.
I believe your current fiscal year of the model is 2020 which means you will store 2019 data as Historical data in DAT03 Historic Volumes. When you Offset these values by 52 weeks they will only populate 2020.
On the other hand If you have Historic Data in 2020 then 2021 will be populated as well because you are offseting the data by 52 weeks.