Swap the feeds to the relays over and you will see if the fault is the really board or the wiring .You can also do some checking with a multimeter or by connecting an led and resistor to the Arduino outputs, or to the connections at the relay board.There is a good chance , if you are switching a big load at mains voltage the relay has failed
Are you using a separate power supply ?This can be quite important with relays as some draw more power than the Arduino can actually supply which will result is a misfire of the relay.Seen this with some of my relay boards and inevitably a proper power supply for the relays fixes the issue.
And a shared COMMON back to the Arduino ? (often required)
A link to the source of the second set of relays would be really helpful.I can't get to the box containing them because it is under my fish tank and it is too cramped but I bought them from eBay and pretty sure this is the one... HereThey sound like higher consumption relays ? I'm sorry but I have no idea what that means. lol. Are you running both groups from the single supply ? Yes I have a 5v supply going into my Arduino housing which then gets sent via Ethernet cable to the relay box about 1 metre away under my fish tank. The one 5v supply goes to both.How would the 5v supply have any effect on it switching on and off? Doesn't the 5v from the Arduino digital pin switch it? (I'm not being funny, I'm just interested in where you're going.)
Are you running both groups from the single supply ?