By default, the Growl messages are removed after a certain span of time. The default lifespan of Growl messages is 3000ms. This can be customized using the life property (that is, life="5000"). To make the Messages as sticky, irrespective of the lifespan mentioned, you should enable the sticky behavior, that is, sticky="true".
PrimeNG Version 4.0.1 supports the two-way binding feature for Growl messages. Due to this feature, whenever the message is removed manually from UI, backend instance, or message, array will be updated immediately.
The complete demo application with instructions is available on GitHub at