Thank you for your answer. What I had to do was indeed to add extra capsules to the finger meshes and to make sure that their collision system was set to block Flex objects.
I have another problem now: the hand meshes appear at the wrong position now. In the screenshot below, the hand is right in front of my character, and it appears closer to his head.
I have tried disabling the plugin/restarting UE4/reenabling the plugin/restarting UE4 and the problem is still there. Even when I create a new project and follow these instructions I still get the error.
This problem appeared when I double-clicked the LeapEchoHands_AnimBlueprint animation blueprint in my project. Before opening it, UE4 told me asked me to rebuild the mesh (or something to this effect) and I clicked yes. Now I can’t get back to the working setup of the leap hands.
Interestingly enough, my project is source controlled and I do not see any changes to the LeapEchoHands_AnimBlueprint file.
Any ideas on how to restore the working leap animations?