As discussed via email, in your scenario a single page seems to cause 400 * 3 = 1200 subscriptions and the bandwidth is 250 / 8 = about 31 kilobytes per second.
In this scenario the bandwidth limit may be hit in peak time.
This would cause intense filtering for the most active items and might cause delays for the less active ones.

In any case, we should analyze the whole history of the internal monitor in order to understand the Server state. Please activate the internal monitor logging, by configuring <text_monitor> to Y and by providing a suitable appender for the LightstreamerMonitorText log4j logger.