Mysterious behavior: keyboard input is repeating some whole words!

As I am typing this message I might have a few letters or even a whole word repeated. So I type:

"repeated"

and I see

"repe repeated"

I've rebooted, removed plugins, changed keyboards wholesale, checked all the accessibility settings that could conceivably be involved and I cannot figure it out. This started happening about a month or so ago. Maybe when I updated to Catalina.

It happens in:

• Browser (Chrome/Brave) (just happened entering this message)
• MacOS Mail
• VS Code

When it happens I think I see something white flash in the bottom left corner of the scree. It happens so fast that I cannot ever move my gaze there fast enough to read what it says or what it means. But there's a connection.

I've deleted all my text shortcuts and other custom keyboard bindings.

Any guesses?

I found the problem. I don't remember the source so help me with the citation if you know it. I uninstalled all Wacom drivers and this solved the problem. Wacom is a pen tablet and I can't imagine what it might have had to do with keyboard input.