Hi @fred_elffin
Welcome to the Forums!
If Zwift on your Macbook Pro is exhibiting the same symptoms as explained in the Forums thread Steve mentioned, then it does seem that your Mac is most likely impacted by that known issue.
I know that this has been flagged up to Zwift’s developers and they’re working on a fix, but to my knowledge there is no solid workaround. Using your iPhone or older Mac might be the best option until the issue can be resolved on our end.