Late 2016 MacBook Pro w/ TouchBar LG Ultrafine 5K display
Screen Sharing app connected to remote instance in the cloud
Very slow response to keystrokes. There is no problem in other applications. The problem goes away if I disconnect the external display. The problem does not go away if I switch from WiFi to a hardwired Ethernet connection. I had thought this might be the monitor's shielding problem interfering with WiFi but no, it happens without WiFi. Truly perplexing!