I've spoken to Development about this and there have been some changes to the touch interface.
Previously the touch interface piggybacked mouse movements, hence pressing the zoom tool and then touching the screen in the way you would with the mouse.
In the most recent update this has changed and the touch interface is seperate. Now to zoom, you simply pinch the screen (pinch-to-zoom), much like smart devices.
You can also pan in the the way you would a smart device.
Please can you try this with your latest software?
If this does not work, please can you tell me:
Operating system & the Software release information (under Help>About).
In the meantime I will check the release notes to see if this has been addressed.
Technical Author @ Pico Technology UK