Can you please upload indexer.log files from all the nodes? After looking at the logs, I can better explain the root cause of the problems, if any.
From the other topics you have created
what I can see is, partition distribution (3, 3, 2) looks fine to me (as mentioned by @prathibha). With partition distribution (3, 3, 2), the ratio 12M:12M:8M seems like a uniform distribution among the partitions.