Please get in touch with us at any of the other support channels – https://helpx.adobe.com/support.html . Since this is not a generic issue that we can reproduce at our end, we will need someone to look into your machine to figure out what is going on here.
Ashutosh Chaturvedi | Sr. Quality Engineering Manager – Illustrator
@Randy Burke - THANK YOU! I was going nuts trying to create a new art brush. I was making it vertical (as I had seen in a tutorial) but for some reason EVERY time I set the direction to run parallel to the line I made, Illustrator made it perpendicular. I finally rotated the object I was using as my brush 90 degrees as you mentioned, and it worked! Now the brush follows the direction I specified when setting it up.
Randy Burke commented
I've seen this issue when a brush is created vertically. It seems that vertical-ness takes over any brush direction given to it. The only fix I've found is to take the actual items you organized into a brush, rotate THEM 90 degrees and make THAT a brush. For me, that's fixed things in the past. Hope it helps! This worked as a work-a-round. suggested by S. Gans
Illustrator CC 22.0.0/macOS 10.12.6
Sarah Khan (Illustrator team) commented
Can you please share your system info with us. As this is not a generic problem and it would help us to reproduce the issue at our end.