Can you please mention the version of HFM and HFM app?
we are on 18.104.22.168.
The first question will be if there were any errors during the upgrade from classic to EPMA?
The second question is if you have tried to load rules?
Please check the Default Frequency for your "Scenario" dimension members. If its set to YTD it would display invalid for the Monthly periods.
Also put all the rest dimensions including Customs in the Data Grid to the base level. Try it and let us know.
Jignesh K Rita