There can be various reasons for a channel not to get registered with the RP.
Check if IP TTL setting on the streamer is sufficient to pass every L3 hop until it reaches RP.
Check if the relevant VAP group has the correct unicast routing towards the RP.
Check if pim-register messages leave the VAP and if pim register-stop messages from the RP reach the VAP.
There are different types of network services that send multicast traffic not supposed to be joined externally.
For example, Microsoft Windows Server clusters use multicast messages and some of them are using TTL equal to 1. If a VAP group running PIM is a part of that network, it will receive the traffic and try to register it with the RP.
If multicast support isn't required on the circuit connected to such network, you can disable "ip pim sparse-mode
" in the PIM circuit configuration. Alternatively, you can create a flow-rule with action drop for that specific multicast traffic so it doesn't reach the VAP group.