Update for anyone experiencing the same problem -
I managed to solve the issue by running the MR Updater a bunch more times, it eventually went from ‘searching for FW device’ to ‘FIRM’. I also tapped a bit on top of the interface near the back outputs/FW ports when it happened to work, I’m not sure if it had anything to do with it or if it was co-incidental…
Once I got the ‘FIRM’ prompt, I reinstalled the firmware and now the interface is recognized. Maybe the FW cable is sketchy but for now it’s working. Moral of story MR816 does not like hot-plugging.