Just an update here.
It seems that the officially released Apex plugins for Maya 2015 and 3dsmax 2015 are not fully compatible with the current Apex version in Unreal. I’ve had interaction with someone at Nvidia/Apex and they supplied me with plugins that seem to be compatible so far with the Apex version in UE 4.6.
UE 4.6 is using Apex version 1.3.1 - APEX_ClothingGPUPROFILE_x64.dll
The plugins in Maya 2015 - Apex 1.3.2
The plugsin in 3dsmax 2015 - Apex 1.3.2
The plugins I now have for both are running Apex 1.3.1 similar to that of UE.
I will report back and confirm that the crashes are gone and things are working properly.