I have a single consumer group

All consumers are already subscribed

I call consumer.subscribe() again on each consumer with the same list of topics

Why?
Why would one do this?
What you're trying to achieve?

what is the reason that it's causing this rebalance

The reason is simple: topic's partition can be consumed by only one consumer from a given consumer group at any time.
Again: topic-partition-consumer group relation to consumer is 1:1

All that also make your move not making any sense.