Increased amount of writes after adding a replica to a non-empty table

Hi!

We've been using DynamoDB for quite some time already and never had any issues with it. We've never used global tables though. Yesterday we decided to add a new replica to a table in us-west-2. The table already contained ~60 million items totalling ~31 GB.

The whole process of adding a new replica was very smooth, taking around 2 hours, no problem there. The weird stuff started to happen after the replica was created. I expected that both replicas would have roughly the same amount of writes that would correspond to the number of writes done by our application. But some crazy things started to happen with the original replica. The amount of writes increased significantly there even though the traffic coming from our application didn't change (see the attached picture). And the application still works only with the original replica in us-west-2.

Does anyone know where these additional writes come from?