Final update, I managed to get through this issue for both showing the mappView visualization on the browser and on the HMI.
For the browser, it was a time sync issue and the way I resolved that was by going into Automation Studio, then “Online” → “Info” → “Date/Time” then select “Set to Target” to transfer the NTP (Network Time Protocol) from your computer to the PLC, which also syncs the NTP for the client/server.
For the HMI, it took more effort, I had to enable NTP server on the configuration menu of the CPU module and on the HMI service page, activated web server on the service page with the address “192.168.0.110:81/index.html” (This is the IP address for the CPU). I ensured that the settings for the AS6 project matched the settings for the HMI, and that the IP address of the HMI was different to the address of the CPU but on the same subnet. Even with those configuration changes, I was still not getting the visualization displayed on the HMI until I updated the Linux Image and the Firmware of the HMI to the latest available. I had help from B&R support on these things.
Hopefully this helps anyone else having these issues.