Hello @DL38, welcome to the forum!
While it is unfortunate that Duplicati doesn’t have a built in point-to-point backup feature like CrashPlan did, it sounds like you’re going about putting together your own solution correctly.
Are computers A and B on the same network or is this going over the internet?
Depending on your Duplicati version you could try adding --verbose=true to your job and try running it from the command line. Or using --log-file=<path> and --log-file-log-level=profiling to get a file full of detail…
Oh, and do your firewalls and ssh servers have their own logs you could check just to see if they register an incoming connection?
I realize OpenSSH is not the same as WinSSHD, but when you set up your OpenSSH servers, did you use any of the info from this How-To topic?