Are you absolutely sure (have tested) that the wifi connections maintain connection to the internet when ethernet ones drop?
Ethernet cables do sometimes fail - but I guess if you have multiple ones fitted they are all unlikely to do so at the same time as you say is happening. However, there have been examples reported here where a switch develops a fault. As 1GB-Unmanaged switches are relatively cheap I would replace it. Unless yours is a high port-managed model perhaps? What make/model is it. You could test it by taking it out of the equation by getting a long run of Cat5e/6 cable (pretty cheap too) and plug your device in that and directly into the Hub and see if the problem persists on that connection.
I would rule those out first, but it's possible that the Hub has developed some fault on the ethernet ports - there have been a few reports on here recently where customers have lost the use of ethernet connections. If that is the case all you can do is call it in as faulty and ask for a replacement.
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John
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I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.