In version 3.2.1 of SFTP Gateway the swap partition is missing upon creation of your VM.
This can be an issue if your memory is being highly uitilized, although it isn't a major issue.
This issue will be resolved in version 3.3.0 of SFTP Gateway.
Rebooting your VM will resolve the issue, this can be done with this command:
Alternatively, if you don't want to reboot your VM to fix the issue you may run this command:
sudo service walinuxagent restart