Could you please let us know the analysis expression you are using and AF version? Also would request you to check AF analysis configuration (i.e. automatic recalculation for selected analyses)
Values from in the PI Data Archive mysteriously disappearing shortly after arrival could be because there is no archive online for the time period. The data ends up in the archive cache, and is lost when flushed to disk. Make sure you have archives online in that time period.
This is the answer, thanks for this.
I agree with Dan, sounds like you don't have archives online for that time period OR you have a corrupt archive.