Hello There! 
I’ve just encountered the same issue. For a temporary “fix” you could try exporting those animations instead of migrating them. Once you reimport them to your current project they should no longer be in A pose. Downside is, I believe and not 100% sure, you loose all the extra data Epic included with these anims, such as footstep notifies. Would be interested to see if anyone found a proper fix for this.