Reproduced 3/3 times, issue does not occur in //UE5/Release-5.0 - CL 20979098 Binary. Confirmed Regression.
I've tried enabling the Media Movie Streamer plugin & Electra Player plugins, but Game crashes the same regardless.
Actual Result: Game freezes on last frame of 1st Movie, then crashes
Expected Result: All Startup Movies should play
Assertion failed: IsInGameThread() [File:D:\build\++UE5\Sync\Engine\Source\Runtime\HeadMountedDisplay\Public\IHeadMountedDisplayModule.h] [Line: 90] UnrealEditor_WindowsMoviePlayer!FVideoPlayer::AddStreamToTopology() [D:\build\++UE5\Sync\Engine\Plugins\Runtime\WindowsMoviePlayer\Source\WindowsMoviePlayer\Private\WindowsMovieStreamer.cpp:619] UnrealEditor_WindowsMoviePlayer!FVideoPlayer::SetPlaybackTopology() [D:\build\++UE5\Sync\Engine\Plugins\Runtime\WindowsMoviePlayer\Source\WindowsMoviePlayer\Private\WindowsMovieStreamer.cpp:573] UnrealEditor_WindowsMoviePlayer!FVideoPlayer::OpenFile() [D:\build\++UE5\Sync\Engine\Plugins\Runtime\WindowsMoviePlayer\Source\WindowsMoviePlayer\Private\WindowsMovieStreamer.cpp:492] UnrealEditor_WindowsMoviePlayer!FMediaFoundationMovieStreamer::OpenNextMovie() [D:\build\++UE5\Sync\Engine\Plugins\Runtime\WindowsMoviePlayer\Source\WindowsMoviePlayer\Private\WindowsMovieStreamer.cpp:266] UnrealEditor_WindowsMoviePlayer!FMediaFoundationMovieStreamer::Tick() [D:\build\++UE5\Sync\Engine\Plugins\Runtime\WindowsMoviePlayer\Source\WindowsMoviePlayer\Private\WindowsMovieStreamer.cpp:218] UnrealEditor_MoviePlayer!FDefaultGameMoviePlayer::TickStreamer() [D:\build\++UE5\Sync\Engine\Source\Runtime\MoviePlayer\Private\DefaultGameMoviePlayer.cpp:729] UnrealEditor_MoviePlayer!TEnqueueUniqueRenderCommandType<`FDefaultGameMoviePlayer::WaitForMovieToFinish'::`28'::BeginLoadingMovieFrameAndTickMovieStreamerName,<lambda_b70ea181931765bdac085d79b561f4be> >::DoTask() [D:\build\++UE5\Sync\Engine\Source\Runtime\RenderCore\Public\RenderingThread.h:206] UnrealEditor_MoviePlayer!TGraphTask<TEnqueueUniqueRenderCommandType<`FDefaultGameMoviePlayer::WaitForMovieToFinish'::`28'::BeginLoadingMovieFrameAndTickMovieStreamerName,<lambda_b70ea181931765bdac085d79b561f4be> > >::ExecuteTask() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Public\Async\TaskGraphInterfaces.h:1348] UnrealEditor_Core!FNamedTaskThread::ProcessTasksNamedThread() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:760] UnrealEditor_Core!FNamedTaskThread::ProcessTasksUntilQuit() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:649] UnrealEditor_RenderCore!RenderingThreadMain() [D:\build\++UE5\Sync\Engine\Source\Runtime\RenderCore\Private\RenderingThread.cpp:415] UnrealEditor_RenderCore!FRenderingThread::Run() [D:\build\++UE5\Sync\Engine\Source\Runtime\RenderCore\Private\RenderingThread.cpp:541] UnrealEditor_Core!FRunnableThreadWin::Run() [D:\build\++UE5\Sync\Engine\Source\Runtime\Core\Private\Windows\WindowsRunnableThread.cpp:149]
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-173500 in the post.