Consider starting "ssh -M -N" separately first, and adding "ControlPath /tmp/ssh-socket-%r@%h:%p" to your ~/.ssh/config file, in the appropriate Host section. This should result in a single ssh connection (negotiated only once) and each file transfer should create a new session only (inside the preexistent connection).
Consider starting "ssh -M -N" separately first, and adding "ControlPath /tmp/ssh- socket- %r@%h:% p" to your ~/.ssh/config file, in the appropriate Host section. This should result in a single ssh connection (negotiated only once) and each file transfer should create a new session only (inside the preexistent connection).