REPOST: Help Quick Please - iMac exporting/rendering shutdowns

I posted this last week but didn't get the help I needed. Here is the original post and below it will be what I'm posting today.

I am exporting an hour-long church service (estimated size 2.8gb) 

My computer specs:

27in iMac refurbished bought online

macOS Catalina 10.15.3

Processor: 3.5GHz Quad-Core intel core i7

Memory: 32GB 1600 Mhz DDR3

Graphics: NVIDIA GeForce GTX 780M 4GB

3T Fusion Drive but I am exporting to a 2TB Hard drive

On OpenCL and hardware encoding, I am using about 60% CPU and on all software settings, I am using around 80% CPU. I have tried exporting on OpenCL and Metal and on both it shuts down. I have also tried encoding on software and hardware and it also shuts down. There are no warning signs of shutting down, or errors when it boots back up. It will just pause for a second and shut down, then restart. It happened about 5 times today no matter what settings I use. Any ideas?

Edit: This might be a stupid idea, but is it an energy impact issue? The energy impact is near peaking as I watch the activity monitor. The export is about 23% in and the energy impact is holding steady at around 750 and sometimes hits 800's, which I near the top. Is it possible for it to draw so much power to just shut off? Which would explain no errors or crash warnings when I power it automatically restarts?

____

I was rendering in-to-out on another hour-long project which was going very smoothly. It was at around 70% and then it just shut down... no warnings no errors just turned off. And no errors came up when it automatically rebooted. It also didn't save any of the rendered previews because I opened the project back up and none of it was rendered. 

Please Help!