I made a short video to explain what’s going on.
this problem also happens when blending from the old ue4 idle anim to the new one, so it can’t be a problem with the animations we have in our project.
EDIT - If anyone knows of a way I can fix this, I would be very very grateful.
This is a known bug with the newer default animations in the Third Person Template reported as JIRA [UE-19659] but there is no estimate regarding when they will be fixed. However, I have added this post to the report and commented that there is increased interest in this bug.
This has been reported fixed for the official 4.11 Release.