Unicast RPF (reverse-path forwarding) configured on the EX Series Switch may prevent Sflow PDU's from being sent to collector. Unicast RPF filters traffic with source addresses that do not use the incoming interface as the best return path back to the source. The interface configuration parameter is "rpf-check".
When configuring Sflow "rpf-check" should be disabled on the interface for Slow PDU's to be sent to collector. This will disable the RPF check. Configuration with rpf-check: