For starters you'll need to confirm that you have IGMP snooping enabled on the VLAN on each participating switch. The command below will show what VLANs currently have IGMP snooping enable. IGMP is a standard protocol, so regardless of the vendor, if you have the same version, it should work just fine
show igmp snoopingNext check to verify the version of IGMP running on each device participating in the multicast stream. IGMPv3 is backward compatible with IGMPv2, but IGMPv2 is not forward compatible with IGMPv3. So if you have a device dishing out v3 INCL, but the device receiving those includes only understands v2 JOINs, it most likely wont work. To verify the version run the following command:
show igmp snooping
Next, you need to verify that the Sender is actually sending the multicast stream and it is arriving on the switch, you can run the following commands to verify this:
show mcast cache
show igmp groupthe show igmp group command shows both senders that are currently active on a VLAN and receivers, if any are currently subscribed.
If your unicast streams are working, I don't see how STP could affect the mcast stream, as far as I know, it cannot tell the difference.
If you're still having trouble with the stream, mirror the port that one of the senders is connected on and run a wireshark capture to see what it is sending. Here's an article on how to configure a mirror in a EXOS: https://gtacknowledge.extremenetworks.com/articles/How_To/How-To-Enable-And-Configure-Mirroring-In-E...
I hope this helps. If you have any more questions, please feel free to ask!