Follow up on this post. (since there was no solution actually posted prior to its close)
community.endlessos[dot]com/t/every-time-i-move-my-mouse-it-lags-drasticaly/22920?u=officecall
I just had this same exact problem both with keyboard and mouse lag on initial install. I was able to correct this by installing an update for Gnome in Settings > About > Software Updates. After install and reboot problem is corrected. Which is strange since I just created the live usb 2 days ago. Running in live mode on usb did not present this issue. It only showed after install on internal SSD.