Dell Inspiron 7537 Laptop Missing Characters When Typing

Machine approaching three years old and not continually used. A couple of weeks ago, it started missing characters when typing or it will type two characters and then highlight them so when you type again the first two characters are gone. Does this on both the on screen and laptop keyboard. Tried an external keyboard and it too acted the same way.

Here's what I've done - run diagnostics (no issues), downloaded and installed most recent BIOS, chipset, video and all other drivers. Have also in Device Manager deleted keyboards and rebooted with no change. All Windows 10 updates are installed.

Most of the time I have it plugged in and charge set to only charge when battery is approaching low.

Have not removed the battery and keeping it as a last option.

Any ideas?