I'm running UE4 4.20.3 and the latest (commit e91d4ee) version of the runtime (3.7-beta-cpp) and found a consistent crash when re-importing animation data.
When I have a map or blueprint open that utilizes a spine animation json/atlas combo, if I drag and drop the .json file into UE4 in order to update it the editor will hang and finally crash. I've gotten 2 similar crash logs while doing this. If I close all blueprints and maps that use that spine animation, then it imports just fine. Here are the crash logs from UE4:
Access violation - code c0000005 (first/second chance not available)
UE4Editor_SpinePlugin!USpineSkeletonRendererComponent::UpdateMesh() [h:\projects\unreal\battlemals.4.20\plugins\spineplugin\source\spineplugin\private\spineskeletonrenderercomponent.cpp:220]
UE4Editor_SpinePlugin!USpineSkeletonRendererComponent::TickComponent() [h:\projects\unreal\battlemals.4.20\plugins\spineplugin\source\spineplugin\private\spineskeletonrenderercomponent.cpp:160]
UE4Editor_Engine!FActorComponentTickFunction::ExecuteTickHelper<<lambda_e8384def656dc646af48282ce274db64> >() [d:\build\++ue4\sync\engine\source\runtime\engine\classes\gameframework\actor.h:3095]
UE4Editor_Engine!FActorComponentTickFunction::ExecuteTick() [d:\build\++ue4\sync\engine\source\runtime\engine\private\components\actorcomponent.cpp:797]
UE4Editor_Engine!TGraphTask<FTickFunctionTask>::ExecuteTask() [d:\build\++ue4\sync\engine\source\runtime\core\public\async\taskgraphinterfaces.h:829]
...
and
Access violation - code c0000005 (first/second chance not available)
UE4Editor_SpinePlugin!spine::AnimationState::apply() [h:\projects\unreal\battlemals.4.20\plugins\spineplugin\source\spineplugin\public\spine-cpp\src\spine\animationstate.cpp:403]
UE4Editor_SpinePlugin!USpineSkeletonAnimationComponent::InternalTick() [h:\projects\unreal\battlemals.4.20\plugins\spineplugin\source\spineplugin\private\spineskeletonanimationcomponent.cpp:100]
UE4Editor_Engine!FActorComponentTickFunction::ExecuteTickHelper<<lambda_e8384def656dc646af48282ce274db64> >() [d:\build\++ue4\sync\engine\source\runtime\engine\classes\gameframework\actor.h:3095]
UE4Editor_Engine!FActorComponentTickFunction::ExecuteTick() [d:\build\++ue4\sync\engine\source\runtime\engine\private\components\actorcomponent.cpp:797]
UE4Editor_Engine!TGraphTask<FTickFunctionTask>::ExecuteTask() [d:\build\++ue4\sync\engine\source\runtime\core\public\async\taskgraphinterfaces.h:829]
UE4Editor_Core!FNamedTaskThread::ProcessTasksNamedThread() [d:\build\++ue4\sync\engine\source\runtime\core\private\async\taskgraph.cpp:665]
...
If I had to guess, it seems like the blueprint actor is attempting to update the animation while the new data is being imported; encountering a null parameter or something.
