Clean Your Phones
As with any technology, keeping it clean will keep it working. We would advise to add cleaning your devices as a part of your daily or weekly cleaning to ensure issues with buttons and sticking do not arise.
Cleaning the devices is rather simple, please take a rag with general cleaning solution sprayed on it and wipe the device down.
If this doesn't resolve your issue, please leave a rag with solution on the device to sit for 5-10 minutes and reattempt until function restores.