In case you experience issues using a chest strap, please try the following:

• Make sure your battery is charged. Issues and erratic sensor behavior are possible on a low battery
• Make sure the chest strap is humid, otherwise contact might be suboptimal. Note that normally chest straps are used during exercise, hence sweat makes it possible to gather high quality data without taking care of preparing the strap before. However, for morning measurements, you should always make sure the strap is a bit wet / humid before using it.