Citus: Parallel worker not launching

We are performing Citus benchmarking and came across a situation where the planner makes the parallel execution plan but during the execution no parallel workers are launched. The cluster has 3 worker nodes each with 2CPUs running on Centos. What can be the reason behind this? -> Finalize Aggregate (cost=76650.31..76650.32 rows=1 width=32) (actual time=174741.832..174741.999 rows=1 loops=1) -> Gather (cost=76650.09..76650.30 rows=2 width=32) (actual time=174741.807..174741.974 rows=1 loops=1) Workers Planned: 2 Workers Launched: 0 -> Partial Aggregate (cost=75650.09..75650.10 rows=1 width=32) (actual time=174740.490..174740.492 rows=1 loops= Query we are using for benchmarking is select sum(amount) from tab_dist_1 where id>=49820 and id<=59743292;