Double Typing on my MacBook pro I've been having this issue for the past few months, where my Mac will echo type whole/partial words while I'm typing. This isn't the same issue as double typing keys, but rather whole phrases will appear again in the middle of me typing. It looks something like this:

"Hello ello world!"

Sometimes it will execute a command to close a window twice.

This goes away when I'm in "Safe Mode". Does anyone have any clue where this is coming from?

I don't think this is a keyboard issue, honestly. Well, maybe a buffering issue? I contacted Apple Support and they didn't have much to say. I reinstalled the operating system, and it still comes up. Though, it did seem to largely go away for a few days.

Additional Details:
Running Catalina 10.15.1 (Happened on previous versions of Catalina too)
MacBook Pro 2017 13inch
There appear to be many variations on this question, that I have found. 

However the problem addressed in this question is the one that I was experiencing. 

So I'd like to try to post here a comprehensive answer that addresses the best possible solutions that have come up so far, starting with all the most common, simplest and least likely to work suggestions up to the ones that seem to address this problem specifically.

Note: If you've done your research, you'll note already an enormous amount of overlap with multiple pages linking back and forth to one another, in regards to this issue. My attempt here is simply to aggregate as many of the key factors involved into one place.

Background

So for a long time now, MacBook users have reported a 'double typing' issue, most especially with the most recent MacBook Pro's to hit the market. There have been many reports of this problem occurring on 2015, up to 2019 edition MacBook Pros, from the 13' to the 15' Touch Bar, and every thing in-between.

There appear to be multiple similar problems, that may or may not have more than one possible solution. The most common reported issues I have seen are:


single keys such as b or n being pressed and outputting doubles like bb or nn in their place. Space bar is also commonly reported to be double typing.
some people may also be irked by the default setting of a double space autocorrecting to a period ..
instances of multiple repeated strings or sequences of keystrokes, at seemingly random intervals, for example whole words, or even multiple words appearing twice, and also modifier commands such as: ⌘+w or ctrl+tab.


In my case the problem was the latter. I'm sure other variations of this problem exist, these are the ones I've encountered most frequently in my search for a solution.

Possible Solutions

This is a summary of most of the answers that I have come across so far, hopefully one of them will work for anyone who is experiencing this problem.


System preferences -> keyboard = Slide the bar left to turn 'key repeat' to off. This is one of the most common solutions as it is by far the simplest and quickest to try. It's also the least likely, from what I've gathered.
cleaning your keyboard, as per these instructions there's even an app to help you do this
turning off the period autocorrect option = System preferences -> Keyboard -> Text: Uncheck "Add period with double space" 


This problem has become so substantial that Apple has released an extended service specifically for this problem, whereby they are replacing keyboards free of charge for anyone who's device falls within their approved list, which as of Jan 2020 includes all Mac products using the butterfly keyboard. 

Like many others however, it seems to be increasingly clear that for most people (though not all) this is not a hardware issue. Many users, including myself, have testified that this occurs not just on the Mac keyboard, but external keyboards also, wired, wireless and bluetooth alike.

Most significantly this problem appears to have started for many, only after installing Catalina.

Users have reported that the problem disappears when:


Running their Mac in 'safe mode' 
In other user accounts on their machine (this is true in my case)


So a number of other suggestions have also popped up. For those who believe that their problem is software related, the following solutions may work for you.


Install an app called Unshaky
Reset your NVRAM as per a comment from this other question


option+⌘+P+R

Update to the latest version of macOS Catalina (version 10.15.3 as of the time of writing) -- System Preferences -> Update Software
Create a new user account
Re-Install MacOS in the Background
Roll back to the previous MacOS, Mojave
And the worst case scenario - A full wipe of your system and re-install a fresh version of your MacOS


For anyone who has Wacom tablet software installed

this Reddit post appears to have isolated a fairly specific problem, but it appears to have fixed the problem for a lot of people, and makes intuitive sense to me, for anyone who has Wacom Driver software in their system.


Install the most recent Catalina compatible Wacom software from their website --(This is what solved the problem for me)
Uninstall any Wacom drivers you may have installed on your system. Official instructions can be found here


disconnect tablet from USB
Navigate to: Finder -> Applications -> Wacom table -> Wacom Tablet Utility
Click the 'Uninstall' button
Restart your machine
Find and delete all related folders as per the linked instructions



Acknowledgements

Finally, I'd like to acknowledge the multiple posts and pages that I have drawn on to find this solution. I can't take credit for any of the solutions posted here, I found them all in my efforts to fix my own frustrating problem. I hope that anyone experiencing this problem finds a solution in this answer.