It is very important to make sure the camera is maintained in a proper way - to avoid malfunction of the hardware.
The camera has to be cleaned after each dive - especially in saltwater. Otherwise, the magnets in the selector ring and activation ring will be subject to rusting.
You should take a bucket of warm, fresh water (for the salt to dissolve fully), and work the selector ring and activation switch for a couple of minutes while submerged.
If you can sense some grains of sand inside the activation switch or selector ring - the parts can be removed and cleaned.
If you are diving often (especially in high salinity waters), it is a good idea to remove the selector ring from time to time, clean the part with a magnet and apply silicone grease on both sides of the magnet.
You can find the instructions to remove the parts in this article.
Note: If you do not have a possibility to clean the camera right away, make sure to keep it wet - so the salt doesn't have a chance to crystallize.
!It is very important not to use any chemicals/cleaning products with the camera, as it might damage the components!