As soon as a listener starts listening to radio online, digital advertising is first played. This is called a pre-roll. After this pre-roll you willhear the regular commercials that the programming of the radio station uses. If you are unfortunate, after the preroll ends you enter while a commercial is also playing at that moment, hence you get the impression you are listening to multiple commercials.
With some radio stations this digital preroll is played once every half hour and with some stations at every stop, pausing and restarting of their stream. For example Nostalgie Nederland does it this way. Unfortunately JUKE has no influence on this and every radiostation has their own way to handle this.