Aurora mysql throttle during writes

I came across a situation where I need expert opinion. Our application ingests data into table A in aurora mysql 3.02 every 5 seconds. This is a write intensive process. During this time, I am using DMS to replicate data for table B from a different source into the same aurora db where table A is located. After few seconds the application queue piles up with many files which are waiting to be written into table A. We have bumped up the instance from 2x - 8x and there is no luck. I cannot relate how writing data in table B affects data ingesting in table A and how do I approach this issue?