Welcome to Zwift forums!
I looked at your session logs on our server for January 5 and 6. I can see several login / logouts on both days from both the Macbook and the iPhone. Each of those “sessions” only lasted a few minutes, so I am sensing this is because of the connection failure, yes? That must have been frustrating.
However, there was one session today (Jan 6) that listed six minutes @ 12:00pm GMT, where the Macbook succesfully registered the Tacx as Bluetooth cadence, power and control trainer sources. Were you able to ride in-game for those 6 minutes, and if so, did you see the avatar move and register distance travelled?
Since you are a very experienced Zwifter, I trust that you know you can not have the iPhone and Macbook logged in at the same time. To define that further, you don’t want the game app running on a second device at the same time to avoid a conflict between two logged-in devices.
If you end the iPhone session, and force-close the game on the iPhone, will the Macbook then allow you to connect properly?