[rrrpiano]

I've seen this happen on my Surface 4 also. If I try to write too fast with the pen it gets worse. I'm thinking it has something to do with the speed of the related pen software and/or the processor/hardware speed of the tablet, but I'm just guessing. I honestly don't understand what software or hardware on the tablet controls the pen. 
My Surface has the i5 processor, I'm guessing that the i7 version would work better.
Also, when the pen's AAAA battery voltage drops over time, the pen's response diminishes. I just remove the battery when I'm done using it to prolong its life.
Hope that helps.