Editor crashes if you hold shift after dragging a marquee selection on anim sequence notifies then select notifies using ctrl

Looks like this all depends on pressing shift after creating a marquee

1. Open QAGame uProject
2. Open asset ProneToStand_Notify
3. Select the notifies and move them to the left on the track so they overlap
4. Press LMB Marquee select both notifies
5. With LMB still held press shift and then release LMB
6. Hold Ctrl and click one of the notifies and attempt to drag.
7. Editor crashes.

Result
Editor crashes when repeating the last 2-3 steps

LoginId:3029b7d441c4af8d59a7f19a2ed84972
EpicAccountId:c062bc1196444421b9529484d3530371

Assertion failed: IsValid() [Link Removed] [Line: 258]

UE4Editor_Core!FDebug::AssertFailed() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\core\private\misc\assertionmacros.cpp:349]
UE4Editor_SlateCore!FWeakWidgetPath::GetLastWidget() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\slatecore\public\layout\widgetpath.h:259]
UE4Editor_Slate!FSlateApplication::RoutePointerMoveEvent() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5330]
UE4Editor_Slate!FSlateApplication::ProcessMouseMoveEvent() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5905]
UE4Editor_Slate!FSlateApplication::OnMouseMove() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5839]
UE4Editor_Core!FWindowsApplication::ProcessDeferredMessage() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\core\private\windows\windowsapplication.cpp:1744]
UE4Editor_Core!FWindowsApplication::DeferMessage() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\core\private\windows\windowsapplication.cpp:2149]
UE4Editor_Core!FWindowsApplication::ProcessMessage() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\core\private\windows\windowsapplication.cpp:869]
UE4Editor_Core!FWindowsApplication::AppWndProc() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\core\private\windows\windowsapplication.cpp:709]
user32
user32
UE4Editor_Core!FWindowsPlatformMisc::PumpMessages() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\core\private\windows\windowsplatformmisc.cpp:1009]
UE4Editor!FEngineLoop::Tick() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\launch\private\launchengineloop.cpp:3151]
UE4Editor!GuardedMain() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\launch\private\launch.cpp:166]
UE4Editor!GuardedMainWrapper() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\launch\private\windows\launchwindows.cpp:134]
UE4Editor!WinMain() [d:\p4\dbouimad_dev-animphys\engine\source\runtime\launch\private\windows\launchwindows.cpp:210]
UE4Editor!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:253]
kernel32
ntdll

Moving a PlaySound notify causes editor to crash