Try test.*. As per the official SFTP document, at least empty should have picked all the files. I would suggest opening a ticket with SAP on this.

What filename pattern is specified in the sender SFTP adapter configuration?

What do you mean by "handle this"? Are you talking about alert configuration?

I take that back, "Send" step can't be used to broadcast message parallelly. I did however use parallel Multicast with 2 receivers, made the first receiver fail and successfully received message in the second receiver. Is it behaving differently for ...

You can use the Send step to send messages to multiple receivers parallelly without using multicast.