Just FYI I experienced this even in v4.30 but managed to fix it.
The video initially played OK in preview but once exported, contained freezes.
What i did was cleared the cached under options > disk by checking clear cache on exit.
I then restarted videopad and exported. The output was fine then.
edit: I also changed screen settings to prevent the screen from going to sleep (I know it should not matter, but somehow it did for me)