There were some issues with one of our clients where an UFL interface was used for data backfilling or for daily use to update data into PI. Data wasn’t looking as expected; especially during DST transition there was some data that was in the source files but it was not in PI. The main issue was because the source files were not observing DST, so when they were processed by the UFL interface it was overwriting one hour of data.
The document attached describes an analysis that was done to understand how DST works and how UFL behaves during DST transition time.
Hope this is helpful!