The RPC timeout in JsonRPCEndpoint/getClient method is 300 ms:
private static final int REAPER_INTERVAL = 300;

This timeout is not configurable, and it can be quite aggressive for heavy-weight operations on OVSDB. This leads to the following exception:
java.util.concurrent.CancellationException: Task was cancelled.

One of the solutions would be to retry if the task was cancelled. However, for operations on OVSDB that genuinely take > 300 ms, this will not work – The task will be cancelled again.