I have a logo that I brought into Illustrator and used the Image Trace function. I then pasted that into a mask for a Solid in AE. I want to start with a semi-circle and then have the buildings rise out of it. I keyframed the semi-circle shape and then keyframed the shape from Illustrator but the shape seems to twist itself into knots in the middle (see screenshots). The keyframes on the left swap over to the right. Any pointers on how I could get this to work properly?
Yes, masks interpolate linearly. You need more keyframes or a different approach. Animate the lines and semicircle separately using effects like linear wipes, radial wipes and/or respective shape layers or effects like Circle.
Mask verticies translate in a straight line from keyframe to keyframe in a straight line. This makes things like rotation look weird. There's a tool in AE that can help solve this problem. It's called Mask Interpolation. Find it under Window>>Mask Interpolation.
This tool will help, but only if you have intelligently moved your mask points and you have set enough initial keyframes.