So this should be fixed in one of the next feed updates including some additional updates to the handling of such pfSense applications.
The main problem in this case wasn’t the handling of the device itself in the SSH functions but a used “tcsh” shell for that specific user which wasn’t handled correctly (by appending a /bin/sh to each command as usual).
Nevertheless from the above the suggestion on gracefully handle such bogus return values when searching for binaries was implemented as well.