Having multiple possible answers in a single drop zones only adds to the score if at least one draggable is set to "infinite". This becomes an issue if the drop zone can only contain one draggable.
Test content: https://h5p.org/node/377855 (issue is in slide 6).
Proposal: Have an "or" clause in scoring. If the settings are as follows:
Drop zone: Multiple possible answers and "This drop zone can only contain one element" setting is enabled .
Draggable: "Infinite number of element instances" is enabled