When you start the prime 95 test you are bottle necking your gpu for information gpu usage drops in turn dropping the voltage. when you stop the test the CPU is no longer getting hammered by prime and is now free to send information back to the GPU in turn making the GPU usage go back to 100% which then needs more voltage.
As soon as you started the intel STRESS test once again hammering the CPU your GPU suffers for information and drops in usage and voltage.
You are causing the issue. Stop running multiple benchmarks opening windows. Start the recording then start unigine valley and then walk away from the computer for 10 min. Dont touch the keyboard mouse move any windows nothing. once you hit run on the test dont touch your computer till its done. you will see dips in the usage when it stops and starts each test other then that i will stay up around 100% usage for the GPU.
Watch this
https://www.youtube.com/watch?v=vRp4DfQA6MU you dont see the guy moving the mouse around popping open other windows or trying to run stress test on his cpu during the benchmark.
when your CPU is getting hammered at 100% by another test you are bottlenecking the gpu because it cant get any information from the cpu, that is why your usage and voltage drop the card doesnt need to work as hard to process the information because it cant get enough.