Well for your future reference, Unreal is ‘z’ up and there’s no way to change it. If you import a character made ‘y’ up, something should be 90 degrees off. If not, you should check your pipeline and see where you’re compensating for it (to know). My guess is that you switched Maya to ‘z’-up at some point.
On my side, the model and animations are made ‘y’ up in Maya, and neither the model nor the animations have any root rotation in them. As a test, after exporting the model into FBX from Maya, right there, I imported the animation data right into the same exact model that I had just exported, just to make sure everything was consistent. Once I applied the animation to my model, I exported the animation into FBX with the same exact settings.
In Unreal, the model comes in upright, but the animations come in sideways. The mystery is NOT that the animation come in sideways. That’s the expected behavior. The mystery is why does the model come in upright. Regardless, since the model is upright, the games plays upright. Since the animations come in sideways, all the animation previews are sideways. Rotating all the animations by hand would be too big of a task for me. In Maya’s FBX converter I tried playing with the axis conversion settings, but they don’t seem to be doing anything (tried it both ways on the model and animations not seeing any difference in either).