The exhibit shows that the write region (failoverPriority 0) is West US, and East US is a read region (failoverPriority 1). Users in East US are reading from the local region, but because the consistency level is Session, reads may not see the latest writes if the write is still propagating from West US. However, the question asks about slower reads than writes.
The most likely cause is that read requests are being served from a different region than the user's location due to Cosmos DB's routing policy. But since East US is a read region, reads should be local. The exhibit does not show multi-region writes.
The typical cause is that reads are not local; but in this case, East US is a read region, so reads should be local. Another possibility: the consistency level Session requires a session token, but that doesn't cause slowness. The exhibit does not specify multi-region writes.
However, a common mistake is that if the account has only one write region, reads from other regions might be served from the write region if not configured properly. But the exhibit shows two regions, so reads should be local. Perhaps the issue is that the client is not using the correct endpoint.
The most likely cause from the exhibit is that the account has only one write region (West US), and reads in East US are still going to West US due to client configuration. But the exhibit does not show client config. Another possibility: the default consistency level Session can cause slightly higher latency for reads that need to check the session token.
However, the best answer is that the read requests are being routed to the write region because the client is not configured to use the local endpoint. But since the question is diagnostic, we'll go with a common issue: the client is using the write endpoint for reads. However, the options need to reflect plausible causes.
Let's design options accordingly.