Before backstitching the bury, I hang the hammock (using care not to pull the bury out) and weight it. That "shifts" the bury into it's final position, then I backstitch. If you backstitch while the bury is relaxed, before loading it, there will be some shifting that could break the threads.
This reminds me of times long ago when I would load a truck for moving. I would drive half a block down the road and slam the breaks. Then I wouldn't have to worry about that load shifting for the remainder of the trip!