A regression was introduced by
HPCC-16051 that caused the deserialization of progress data from a group activity in a child query to crash thormaster.
Previously the master activity on the master was created and initialized when the child query was 1st executed on the slave,
HPCC-16051 avoided the initialization call.
The master group activity create required stats. objects used in deserialization in the init function, they should be moved to the activity constructor (as in other cases).