Can you please check RSSTATMANREQMAP table entries where DTA_DEST as your DSO2 and paste here?
I will not say the DTP is missing those alternate requests - still you have a seperate requests with 0 records into DSO 2.....so the issue is somewhere.
I see a pattern of all missing requests has small volume, but it's beeing pulled as 0 records. So did you check if those requests are actually holding data in DSO1?
Did ever any selective deletions happended on DSO1? it's been there for long time..you never know..
Also Do you have any selections or filters on DSO1 -> DSO2 DTP?
Thanks,
Arun