Since this connection was working before, and you are able to see TabPy locally, the data seems to point to this being a networking issue.
Are you able to ping the machine on that port from your laptop: How to Use ping on Mac: Pinging Websites, Domains, or IP Addresses
Thanks for the response. I did a port-scan check using the network utility (Mac) and the port isn't showing as open, despite the fact it is showing as open when I use any port-scan website to see it. Very strange.
Must be a networking issue, then - thanks for the steer!