Are you using USB or bluetooth?
I had all sortsa issues with characters vanishing over bluetooth, and it turned out to be a bad solder joint between espruino and RX pin on HC-05.
@DrAzzy started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Are you using USB or bluetooth?
I had all sortsa issues with characters vanishing over bluetooth, and it turned out to be a bad solder joint between espruino and RX pin on HC-05.