COUNT(ds) > 100
is often converted to
COUNT(CHOOSEN(ds, 101)) > 100
To prevent excessive readahead.
However if the activities are stranded, that is going to cause problems because the CHOOSEN will prevent any strands to be shared between ds and the count. I think it requires an attribute on the CHOOSEN to indicate it is an optimization, rather than a requirement, and a stranded version of that optimization-choosen.