you have asked 2 separate questions - the first just means that you have data that is aggregated (that is it is sum(), avg() in Tableau not that the value is an annual value) and data that is not aggregated in the same formula. If you have blended data any data from the second source comes into formulas as aggregated - probably the source of the issue - so you would need to aggregate the data from the primary source - like min(), max(), atr() would also work
as to the second question it depends on the data and how it is structured - would need to see the data in teh 2 files please attach your twbx workbook
It depends on the calculation you are trying to create.
Check the below link:
There are some data blending limitations around non-additive aggregates, such as COUNTD, MEDIAN, and RAWSQLAGG. For more information, see Troubleshoot Data Blending.