After monitoring my temps from NZXT CAM and from my MoBo LED display, i too get different temp readings for both of them.
My MoBo shows my CPU idling at 34°C while my NZXT CAM shows my CPU idling at 28°C. Speccy also states that my CPU is at 28°C. Since i use more than one software to monitor my temps, i figured out why there's a temp diff thanks to the HWinfo64.
In HWinfo64, the 1st CPU core (core #0) does idle at 28°C while the whole CPU package is at 34°C, just as shown by the MoBo. So, that's from where the temp diff comes in since they display different temp readings from different sensors.
Here's link to the HWinfo64, so you can confirm if it's same for you too,
link:
https://www.hwinfo.com/download.php
(run it in "Sensors-only"...