It looks from that picture like you are not moving your throwhand under the yoyo during the pop from the split-bottom mount back to the mach 5 mount.
When you are in the split-bottom mount, you pop the yoyo up straight up into the top string and then move your throwhand forward and your non-throwhand backward, right? When you do that, you have to pass your throwhand underneath the yoyo while the yoyo is still up in the air. If you let the yoyo drop first so that your throwhand passes over the top of the yoyo, you will end up in the mount in your picture. It takes some confidence to get it right because you have to pop the yoyo up and cross your hands in one smooth motion, but once you know what to focus on it should hopefully start to click.
The other thing is that when you move your throwhand forward, it has to hit the front string. If you miss that string with your throwhand when you cross your hands, you’ll end up in something like a braintwister mount, so that could be what is happening when you get that.