Figured out another bit of information which might help trace the problem a bit better.
After trying to find all sorts of solutions to getting SFTP working, I decided to try another method of SFTP. I've found out that the FireFTP plugin for Firefox is apparently unaffected by this, and can work with the NetGuard off. So it looks like it's less of a global networking issue, but more of a program-specific issue.
So yeah, extra info I think might be of some help.