This answer applies to R4i Mk2
On the front of the R4i remote control, there is a small clear lens which should protrude slightly from the main body. If this lens is inadvertently pushed back into the remote body then this can interfere with the action of button 3. This can be easily fixed by removing the back of the remote control. Please contact us ;if you need detailed instructions.
If not, please do not hesitate to contact us via our support enquiry form.