RouterOS 6.9 IGMP proxy stop working

fast-leave will always do that. Fast leave is only good you have 1 customer connected. If you set fast-leave - router will not do query back if anyone else is listening to the stream. And just stop the stream over the interface, send PIM unsubscribe on upstream. You have to set fast-leave=no and query-response-interval to some as small as you can value, so that your STBs have enough time to respond.