When the benchmark is running, it is fully loading the CPU cores. The TS Bench benchmark does not load the iGPU. This should allow the CPU to run faster. As soon as the TS Bench benchmark ends, now the available power has to be shared between the CPU cores and the iGPU. When there is less power available for the cores, they are going to have to slow down.
The 7100U has a 15W TDP rating. The manufacturer of your laptop might have set a hard limit of 17W. The power limits can change depending on if the Intel GPU is being used or not.
These CPUs also have a configurable TDP mode. In TDP-down mode, the TDP drops to 7.5W.
Intel® Core™ i3-7100U Processor (3M Cache, 2.40 GHz) quick reference guide including specifications, features, pricing, compatibility, design documentation, ordering codes, spec codes and more.
ark.intel.com
Some computers with these configurable TDP chips can get forced into into TDP-down mode for any reason.
The in game on screen stats are not always accurate when a CPU is power limit throttling. Turn on the Log File option in ThrottleStop. Play a game for at least 15 minutes and then attach a log file to your next post or copy and paste the data to
www.pastebin.com
Post some screenshots of how you have ThrottleStop setup.