GS 724T v3

I have installed Five switches in my network model GS724T and configuration was made as follows:

1. Vlan 115 for Multicast data - port 3 to port 12 

2. Management of equipment - port 13 to port 24

3. Port 1 and port 2 - Trunk accepting vlan 1,115 and 116

4. RSTP was selected for all and level 1 for all 

5.bridge priority was set according starting from priority site 4096 and last site is 20480

6. to generate the multicast for radio broadcast, i have to main site but valn is same 115 on both switches installed on the main sites but bridge priority is 4096 and 8192

my issue we lost the multicast service for approximately 15 min and then return back on its own several time and the Net gear log does not see any abnormalities but the encoder log have Ip transmit error

Kindly anyone can advise why this and a solution