Just in case it saves anyone else some time, my Mokerlink 2G04210GSMX (4x2.5G, 1x10G SFP+, 1x10G RJ45), hardware version HS72_V1.04, firmware V1.8, has a bug with the IGMP Snooping functionality.
It works correctly for a couple of weeks or so, and then gets stuck and shows no entries in the IGMP table, which means anything connected to the switch won't get multicast traffic from other ports. Rebooting the switch immediately fixes it, multicast groups show up in the IGMP table and traffic starts flowing correctly.
I haven't tried upgrading the switch with the 1.9/1.91 firmware (which Mokerlink haven't published anyway), as I don't have much multicast traffic I just disabled the IGMP Snooping function so that any incoming multicast traffic goes to all ports. But just a warning for anyone who does have a lot of multicast traffic that the snooping function appears unstable, at least for me.