Slow grouping can be due to:
1) Checking of inventories (they are not pre-profiled). Inventories have only chemicals and have no data. Please uncheck them to be sure that you are only using cached profiling results.
2) Using of private database imported by user. In this case the new dbs need to be cached which is a one time process. After that, grouping will be very fast.
3) Make sure the following option is checked: