Weird random crashes

I have got many random weird crashes recently. I have been working on my project few months without any issue. Was currently working on AI, perception system etc. and had no problem but many random crashes suddenly appeared. Here is one of them which look the weirdest for me related to PhysX sqaabbtree.cpp library.

When I put many AIs who start killin each other it work fine. When AI died, it become simulating ragdoll physics (tried even with no ragdoll simulation but crashes aswell). Even when there are tons of ragdolls simulated it work fine but at random point it crashes. [link text][1][link text][2]

I also included 2 more random different crash logs. Any Idea ?

[2019.06.22-16.22.24:897][262]LogWindows: Error: 
[2019.06.22-16.22.24:897][262]LogWindows: Error: Fatal error!
[2019.06.22-16.22.24:897][262]LogWindows: Error: 
[2019.06.22-16.22.24:897][262]LogWindows: Error: Unhandled Exception: EXCEPTION_STACK_OVERFLOW
[2019.06.22-16.22.24:897][262]LogWindows: Error: 
[2019.06.22-16.22.24:897][262]LogWindows: Error: [Callstack] 0x00007ffecd6bb937 PhysX3PROFILE_x64.dll!_createParentArray() [d:\build\++ue4+release-4.20+physx_compile\sync\engine\source\thirdparty\physx3\physx_3.4\source\scenequery\src\sqaabbtree.cpp:465]
[2019.06.22-16.22.24:899][262]LogWindows: Error: [Callstack] 0x00007ffecd6bb93c PhysX3PROFILE_x64.dll!_createParentArray() [d:\build\++ue4+release-4.20+physx_compile\sync\engine\source\thirdpart
[2019.06.22-16.22.24:912][262]LogExit: Executing StaticShutdownAfterError
[2019.06.22-16.22.24:915][262]LogPhysics: Error: PHYSX: (D:\Build\++UE4+Release-4.20+PhysX_Compile\Sync\Engine\Source\ThirdParty\PhysX3\PhysX_3.4\Source\PhysX\src\NpScene.cpp 238) eINVALID_OPERATION : PxScene::release(): Scene is still being simulated! PxScene::fetchResults() is called implicitly.
[2019.06.22-16.22.24:930][262]LogWindows: FPlatformMisc::RequestExit(1)
[2019.06.22-16.22.24:960][262]Log file closed, 06/22/19 18:22:24

After many hours of painful tests it seem that problem was in setting AnimInstance for Skeletal mesh to NULL (Mesh3PComponent->SetAnimInstanceClass(NULL);). When I removed it the crashes are gone(I HOPE)… It’s anyway weird