Setting decoder to 720 instead of 704 should cause no issue.
As you are using quite old release I am attaching sclrLink patch since DVRRDK 3.5 Pls include all the fixes in your codebase although none of them are likely to resolve the issue you are seeing.(Please visit the site to view this file)
The pitch of scaler output is 1408 because output is YUV422I and your output frame width is 704.
It appears scaler is not using the dec startX,startY at all.
Pls share the console logs after removing nsfLink and include Vsys_printDetailedStatistics.
Also add Vps_printf in SclrLink_drvUpdateRtParams and print startX,startY,pitch,width and height