Broker is using 100% core's CPU time if message grouping is used

When consuming messages with message grouping set on the broker seem to consume excessive amount of CPU time. On 12 core CPU it can be observed that one core goes 100% and stays that way as long as there is more than one consumer attached to a queue. Once the number of consumers is reduced to 1 the CPU usage goes to normal. But moment another consumer is attached another CPU core goes 100%.