Scroll down and read the section "going super cheap".
https://www.techspot.com/review/1603-intel-b360-chipset/
The issue is because Intel's TDP rating is for stock settings. When the CPU boost, even the 8400, the TDP goes beyond the 65 watt rating Intel has for the CPU. The cheaper mother boards were not designed to manage the power required to hold the CPU's boost. So when the CPU hits the VRM power limit, it will down clock.
This would be much more prevalent on a 8700 because it has a higher TDP and has higher clocks. But dropping to a 310 motherboard, even the 8400 turbo can be impacted because it still is a 6 core chip.