problem with switching iptv channels

[dmankg]

hello all,

boss wanted to install iptv in hotel.
we have bought some dvb-ip streamers which r sending multicast streams in udp.
channels comes like udp://@224.12.0.1 3000 first channel
udp://@224.12.0.2 3000 second and so on.

everything works fine except one thing.
sometimes when guests switch channels with vlc. player is not stopped or crashed it seems like it can not catch udp stream or something and looks like simple pause. vlc usually before playback new playlist item shows that it buffering streams. but in this case its just pause.
i did not understand why.
then if i switch to next channel vlc acts fine, buffering and showing iptv channel.
if i go back to previous channel which vlc failed to show now everything is ok vlc buffering and shows this udp stream.

i am sure that this is because incorrect configuration.
please some advices needed to make guests change their channels stable and smooth.

regards,

silem