Hi - I would suspect a faulty switch or cable, or a misconfiguration of the switch (if it has any configuration) . My Sonos units are connected via 4 or 5 switches to the core, and work pretty much fine. Can you try with a different switch and see what happens?
Hmm. Then perhaps some IP address conflict somewhere . . . Hopefully someone a bit more network savvy than me will come along and chip in shortly. Meantime, you might want to provide as many details as possible about your actual setup; it may reveal something obvious - good luck.