I am having this issue with File transfer Activity, where it fails every other day with a timeout error.
What is strange is it does not run for long before I get the timeout error.
The SFTP external account used for this is the one that we use for other FTPs as well and this error happens a couple of times every week ( and not every time) for this daily technical import workflow.
I was not 100% sure how to use the curl to change the timeout issue.
However, we used an alternative approach by creating a technical workflow that checks for the error message, log date and status of the failing workflows and signals to restart the failed workflow again.
I might also suggest increasing the logging to get some more details around the failure. Also if this is happening regularly at the same time, you could set up a pcap/wireshark to analyze the network connection from Campaign to your SFTP.