My first test flight, I was seeing the same thing. It would sort of waffle back and forth. Also, I would occasionally get an error that said the GoPro needed upgraded before it would work with the gimbal. I was trying to use Solo the same as before, taking off from grassy fields and uneven surfaces. I assumed I screwed up during the installation, and was a bit frustrated.
In the online gimbal installation instructions it says (
Gimbal Installation | 3DR | Drone & UAV Technology):
"Caution: Keep Solo level while powering on. Don’t touch the gimbal while it initializes. This can cause the gimbal to calibrate incorrectly and trigger an error."
My second test flight, I took it to the roof of a parking garage so it would be on an even, flat surface and nothing would touch it while it started. This time, Solo and the gimbal worked flawlessly. The video is smooth, and the remote GoPro controls worked. I went through two batteries. The second time it started wasn't as smooth. So, I did have to reboot Solo (turn it off and back on) until the Gimbal did initialize correctly. Then, it was fine again.
So, in my experience, the gimbal is a little finicky. Watch for it to go through its initialization sequence, and make sure it's on a flat, even surface while doing so.