Thanks for the video Alex. Always much easier to deal with a video than with a vague problem description.
I managed to reproduce this freezing and I know the reason for this, however, it'll take me time to think of how to fix this.
The program freezes when it has to settle multiple markets all at once after you move the timeline slider and restart Time Machine. You will notice that a lot of markets become grey in the market list on the left. That means they become Finished and need to be settled, i.e. their winners must be determined. Settling a market takes some time and processor resources. When there is a queue of markets to settle (you have lots of them, so the queue is long), the program may freeze (i.e. stop reacting to the user input) in order to complete this task. Once it can resume its work, you will proceed from where you were before that.
In real life, when trading on BetFair, you don't have this situation because events take place one after another and don't finish all at once.