A lot of the documentation in regards to Cubemaps is very outdated. For instance, on this page (https://docs.unrealengine.com/en-US/…aps/index.html) the alignment of the 6 tiles when preparing an image in photoshop for export to DDS using NVIDIA Texture Tools appears to be incorrect. Aligning all six tiles right side up will produce a perfect result when importing into UE4 (I’m on 4.25). Also, the ‘32bits/Channel, 8.8.8.8 ARGB 32 bpp, unsigned’ preset in Texture Tools Exporter no longer exists. I used “32bits/Channel, 8.8.8.8 BGRA unsigned”.
Honestly the entire process of generating a cubemap from an equirectangular projection and using it to create a custom skysphere material (using the BP_SkySphere object) was tedious. I finally found the solution on some random youtube tutorial with only hundreds of views. I feel that most pages that are labelled as “Unreal Engine 4.9” are severely outdated at this point and could use some tender loving care 
Thanks for your hard work everyone!