This is a regular and longstanding crash in 4.17 that has occurred since at least 4.14. Users have not provided any descriptions of their actions when the crash occurred.
There has been some previous discussion related to this error message in [Link Removed] (auto-expired).
repro steps currently unknown
Assertion failed: OLEReferenceCount == 0 [File:D:\Build\++UE4+Release-4.17+Compile\Sync\Engine\Source\Runtime\Core\Private\Windows\WindowsWindow.cpp] [Line: 557] Not all references to window are released, 1 left UE4Editor_SlateRHIRenderer!FSlateRHIRenderer::DrawWindows_Private() [slaterhirenderer.cpp:989] UE4Editor_Slate!FSlateApplication::PrivateDrawWindows() [slateapplication.cpp:1492] UE4Editor_Slate!FSlateApplication::DrawWindows() [slateapplication.cpp:1188] UE4Editor_Slate!FSlateApplication::TickApplication() [slateapplication.cpp:1773] UE4Editor_Slate!FSlateApplication::Tick() [slateapplication.cpp:1591] UE4Editor!FEngineLoop::Tick() [launchengineloop.cpp:3278] UE4Editor!GuardedMain() [launch.cpp:166] UE4Editor!GuardedMainWrapper() [launchwindows.cpp:134] UE4Editor!WinMain() [launchwindows.cpp:210] UE4Editor!__scrt_common_main_seh() [exe_common.inl:253] kernel32!BaseThreadInitThunk() ntdll!RtlUserThreadStart()
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-48694 in the post.