I've had similar setups in the past, but with Windows 10, there was a "barrier" that prevented me from moving the cursor in that direction. Now, the cursor just pops up at the bottom every time.
Whenever I scale down my main monitor or scale up my other monitors, it results in erratic resolution switching every time I start a game in fullscreen at 4K. This also causes parts of my display on the other monitors to be cut off.