Here are few things to look out for when experiencing a slow WAN performance.
Use the Benchmark Tool to ensure the hardware can provide the required throughput.
Ethernet Interface Settings
Link errors and Duplex mismatches will negatively affect performance.
In version 3, expired keys will cause optimized traffic to be limited to the Express capabilities.
In version 4, expired keys will switch traffic to Bypass/Passthrough.
Datastores get out of Sync
This is possibly due to sub-optimal configuration or a Datastore being cleared on a single end. The slow down will be evident until both Datastores are synced. One method to avoid this slow sync overhead is to clear the Datastore on all peers. Navigate to Configure > Reset > Reset Datastore in Wanos Web UI.