Row validations frequently fail with either "source/target_column_name" as "null"

Tool was running fine with no issues but in O/P I see "target_column_name": null & "target_agg_value": null .
I was trying to compare rows for given primary keys & following below syntax.

> data-validation -v -ll DEBUG validate row -sc BQ_CONN -tc BQ_CONN -tbls pa-dev.bgp_status=pa-dev.bgp_status_v2 --filters 'event_time >= TIMESTAMP_SUB(CURRENT_TIMESTAMP(), INTERVAL 10 MINUTE)' --format json --primary-keys tenant_id,cloud_instance_id --comparison-fields cdl_region,instance_name,node_type -rr

Please help me understand what I am missing here !?