A few thoughts......

-Make sure the camera is going to sleep or turned off between motion events.
-I'm not familiar with the Tether Tools ONsite Relay A. It may be drawing power when the camera is off between motion events.
-I looked at the Tether Tools website. It looks like the adapter has a USB A connector that plugs into the USB A jack on the Cygnett power bank. On the power bank you have one USB A and two USB C connections. The USB A connection is capable of 3 Amps of power at 5 Volts. The Tether adapter then converts the 5 Volts to 7.2 Volts to power the camera. Some power packs power off when they don't detect a load and will not power back up when needed. You might check that by setting up your camera trap at home and running it through many motion events.
-Another way to power the camera is with a battery pack made to power cameras. The Sony NP-F type batteries put out 7.2 Volts and will not need any conversion. This type of power pack is on all the time with no internal electronics drawing power.
-Most USB power packs don't put out the advertised rating. Take a look at this forum thread about testing batteries and power packs. https://www.cameratrapper.com/showth...and-capacities

Hope this helps. Let us know what you find.