The app crashes (freezes then must force-close) for me more than 50 percent of the time I play. This can happen even in the first few waves. I am uploading some screenshots from today where the game crashed twice. I will try and find the "logcat" file you mention in another issue. I will use the "send logs" feature and quote this issue number, hopefully that's useful. I also lose sound at some points but I see that may be resolved.
I have experimented with the speed but haven't noticed a correlation as it can happen when I slow the game down too.