The application is really slow when trying to match move

I have made an icon of a man walking from left to right, by using shapes in Motion. It's a really simple animation and it doesn't take much processor power to render, as it is all made by shapes.

Although, as soon as I match move different body parts, e.g. lower arm matches the movement of the upper arm the application, Motion, just slows down and I have to wait for the spinning wheel for like 30-60 seconds until I can make any further adjustments. And as I try to make any further adjustments as soon as the spinning wheel has disappeared, it comes back and it's impossible to follow how much I'm adjusting something, e.g. the rotation of the upper arm.

There must be a bug in the application. I have a 2018 MacBook Pro, 3,1GHz Intel Core I5, 16Gb RAM, and macOS High Sierra 10.13.3.

I have tried to hide all other objects in the project and also changed render settings to Resolution: Quarter and Quality: Draft, and nothing has changed. So obviously this isn't a hardware performance issue.

Please help! This bug is really annoying and it makes the workflow die completely. I can't wait a minute every time I need to make the slightest adjustment to two simple shapes, regardless of what the adjustment is, only because they are matched moved one to another. It's madness!

My Motion version is 5.4.1