Hi. I’m using the latest version of Infuse 5; I regularly connect via SMB to a Windows 10 machine with both my iPhone 7 & iPad Air 2 (iOS 12.1.3). Occasionally one device or the other will show an error when attempting to connect to a saved Windows SMB share. Sometimes rebooting the device solves it, but not always; sometimes rebooting the Windows machine seems to solve it, but not always.
As I say, it’s intermittent, and often one device will be able to get in but the other won’t. I’ve assumed (correct me if I’m wrong) that there may be a connection limit or lock, so I never try to connect with the iPhone if the iPad is already connected, or vice versa; thus I don’t think that’s the problem.