As far as I know, OBI MV1 tend to heat while charging as well as using wifi hotspot of any SIMs. It doesn't matter whether it's a Reliance Jio or any other SIM card, if you use charging and mobile hotspot (WiFi) together, the device would get heated after using it for a few minutes.
I would recommend, do not charge and use hotspot together. Try to avoid it as much as possible. If possible, keep the handset away from your body and away from clothes or bed surfaces, as the airflow near the handset might help you in reducing the heat.
Longer WiFi hotspot and longer video/game playing could heat the device. It's nowhere related to the camera, unless your camera is being used at that time. Mostly, the WiFi network related chipset is being placed near the camera in the back of your phones, and when the excessive usage of hotpost occurs, then that part of the handset gets heating up.