We can see there are two numeric fields there,
eg: product_a_id and product_primary_genre_id.
There are some known issues with index size bloating which got fixed in upcoming releases of CB server.
One workaround you could plausibly explore is the suggestion specified here with the index definition.
So, you could try creating a newer index with higher number of partitions with the above store property overrides for verifying the index size impacts without impacting your current index.
As @abhinav mentioned, creating a customer support ticket would be the way to go.
Cheers!