I recently purchased the Breville Barista Pro and it has been an absolute nightmare. Can't get my coffee to be consistent and have wasted so much time, energy and money on learning how to use it.

Here's a question...I hope someone can help with this!! I purchased Colombian Roast from a local coffee shop a few weeks ago and was able to make perfectly extracted espresso with these settings:
Grind: 16
Time: 28 seconds

A few weeks later, I buy the same exact Colombian roast beans, and the grind comes out way too course at 16, with my espresso being under extracted. I took it down all the way to 1 and it's still way too course so the espresso comes out under extracted. I've never seen such an inconsistency before. Is it the machine?? Is it the beans?? What am I doing wrong here??

For other coffee beans I've used in the past, my grind setting has always been between 10-18...never lower than this.

Are you weighing the beans in the portafilter, not just using the timer?

Being different by 1 g can make a large change, sometimes even 0.5 g of difference. Changes in roast, batches of beans can change the hardness of the beans and how much is ground in X seconds.

It's hard to think of something that shifted suddenly, but the inner burr can usually be user adjusted

Edit: Another thing might be "too fresh" beans. Sometimes if they are only a day or two from roast, the gases trapped inside the beans from roasting haven't escaped enough yet. Espresso is more sensitive than pour-over as there is nowhere for the gases to go like there would be with an open bloom.