This is normal behavior. You have a PNG with transparency on V2. Therefore, it has work to do to blend it in realtime. It is not a perfectly optimized program. Settings > GPU Effects makes this processing faster, but it also makes the program crash much more.
When I disable it though the audio just becomes completely messed up though.
This is due to a bug in version 18.09. It is fixed for the next version 18.10 coming real soon.
Also it always crashes
It is not perfect, but we keep trying to make it better. You need to provide the steps that caused the crash, or you have to wait for a developer (all 2 of us) to experience the problem ourself and try to fix it. As you can image, we spend much more time working on the code than editing video.