I use an Intel i3-7100, released in 2017, 3.9GHz, 3MB L2 cache, dual core with HT (4 threads)
Over 95% of the time, all 4 threads are more than 70% idle. Only occasionally, one of the four threads drops to 40-50% idle.
After starting the program, the micro freezes (or frame drops?) during passing a gate occur only max. once per gate. Also, I have to pass the gate relatively fast. The issue is present in "forest" but I do not notice it in "dessert". There is no issue, when I pass the gate a second time.
It is possible that all this has to do with using an integrated graphics card (resides inside the CPU) or with some Intel driver in particular.
Edit: This post describes the situation during measuring the GPU utilization. Without measuring GPU utilization, forest is unplayable.