Sorting activity not working in iOS

Hi, I've come across a similar issue, but not for iOS I believe. I've created some Rise modules containing both Sorting Activities and Matching. Neither works on my customer's desktop devices. They've found that it isn't possible to drop the options into place - whether placed correctly, or not for the Matching interaction. They are finding that they 'stick' on the mouse cursor and then just return to their original position when they do free up. They work fine for me, and having tested via both the Review area and my AWS account one of my customers reports that it's an issue in the Review area, but not AWS. Can you offer some advice about any known limitations when using these draggable types of interaction in Rise, please? What might be causing this? Thanks.