it is not a bug but the game is depend/hungry on your CPU not the GPU so you can try those settings and see if it's becomes better gameplay and you can always restore GPU back to its default settings if the performance is worse then before...
*turn on windows hardware-accelerated gpu scheduling feature(this game doesn't seem to like the GPU work for the game so use this feature to share the CPUs task with the GPU)
*turn off all GPU optimizations including all antialiasing mode(AA) and the anisotropic filtering
*set texture filtering quality to high quality and turn the negative LOD bias to clamp
*turn on anti-lag/low latency mode to ultra(this prevent/limited the game to queue frames due to the heavy loads by the CPUs especially while you are on saving/loading RPGM game not sure about the auto-save its probably just the same better to keep it off seem like some bug to me even after turned it to off)
*turn on/off triple buffering and vertical sync to on/fast(all of the vsync mode may have its own issue depending with the monitor but am prefer adaptive(half refresh rate))
*set the virtual reality pre-rendered frames to use the 3D application setting
*you can also enable the performance mode in the game settings to reducing the CPUs task in the game if needed
and yes my pc is older for this game but it still can be playing without the performance mode enable i'd like to watch tia chopping the tree