When COUNTS_DATE is shown as null, it just represents a lifetime count of the virtual service (versus counts accumulated on a specific date ). So when the model stops you would see it change to 'null'
Note** It should be safe to remove anything from VSE_METRICS_TXN_COUNTS. The table only has reporting data on the amount of traffic a VS has handled. you might want to stop all the running VS’s before deleting any rows, to prevent the VS cache from getting out of sync with the database.