When a connection is established using SSL or TLS, regular checks of source port and IP address are required. If inconsistencies are found, termination will occur. Some load balancing scenarios can trigger this when traffic is aggregated over multiple uplinks.
The MX series link aggregation handles this by pairing a single data stream to a single uplink. In other words, once a TCP connection is established between the source and destination, the port and IP address pairing is mapped to a single uplink to prevent the stream from being distributed out another uplink which could result in the connection being terminated by the remote host.