I imported a .fbx file with its animations, but when I choose an animation, the rig is flipped upside down.
However, when I create an empty animation then the rig isnt flipped upside down
UPDATE:
Thanks to UnderTheBridgeGames I was able to fix this issue. When exporting the model, change the Forward property’s value from -Z to Positive Z and it will work!
Awesome, glad it worked out - thanks for posting, hopefully this will help out anyone else encountering a similar issue
In my case the issue was that in “Import 3D” under “Animation General” I needed to have “Rest Pose Animation” as “Default”, instead of “Default with rotations zeroed out”.
currently facing this issue, none of these solutions are working 
Try manually exporting the animations from blender as .fbx one by one, and make sure to play around with the Forward property before exporting. This has been the solution that I’ve been using lately.
that worked! importing animations through the 3d importer is a little messed up 
I had the same problem, when exported model with animations from Blender and imported them to Roblox Studio. But when loading the animation, the model was flipped upside down while animating.
My solution was to export animations as NLA strips, and untick All Actions.
Nice tutorial I found that explained it to me: " How to Export Animation From Blender For Game Engines Like Unity or Unreal" https://www.youtube.com/watch?v=kUn4jUj4gOk
