Spacebar double press on MacBook Pro 2017

Before going a far as reinstalling the OS, I would recommend first trying to just recreate your user account:

• Backup or make a copy of your effected user folder.
• Login as another user other then your old effected user.
• Delete you old effected user account and then delete or move the old effected user's folder out of the /Users folder.
• After the old user folder has been move or delete, recreate another user with your old user name.
• Login as the new user
• Copy all the files/folders you want from your backed up old user folder (but none of the files within old user's library folder)
• Then use this new user going forward.

But it you really want to reinstall the OS then:

• Backup everything
• Doing a clean install of the system without keeping your old user account.
• And creating a new user in the freshly installed OS
• And only restoring the user files you need without restoring any of the user library files/folders

Either way, you may have to reinstall some third-party software as well.

If you try to keep or restore your old user library files you may end up keeping the issue. Some files in the library may be ok to restore but we don't know which one

You can use Time Machine to restore individual files, but I would not do a full restore of everything using time machine as you may end up restoring the issue too.

For info on reinstalling the OS take a look at this Apple Support document which talks "About macOS Recovery"

But again I would avoid the Time Machine recovery. You can also probably find more info via Google on the subject of macOS recovery

https://support.apple.com/en-us/HT201314

I assume you did try changing the "Key Repeat" setting to a slower setting and also setting "Delay Until Repeat" to a longer delay. Both are in the Keyboard PreferencePane. I would also check to make sure Sticky Keys is not enabled (but I don't think this is being caused by sticky keys)

If the above has been done, I would look to see if the spacebar key is getting stuck and is not releasing the key press quickly.

If you truly believe it is not getting stuck in the down position even for a short moment, and that this is a software issue, Try booting in safe mode and see if you problem goes away while running in safe mode. If this works then it may be that you have some Third-party software install that is causing the issue.

You could also try another keyboard and see if the second keyboard has the same issue. As it just might be you have a faulty keyboard

You also might want to try disconnecting and external devices connected to the computer. Like a usb harddrive, etc. and see if that make the issue disappear.

Sorry, totally missed the part where you said you tried a new user account. My bad.

Working in safe-mode tells me it probably has something to do with third-party software installed on your system.

Working from another user account is a clue that it could be a corrupt user Preference File or Cache Data in the effected account. And that this is most likely not an issue with your base OS. You could just keep using this new account since it appears to be unaffected.

So at this point I would be looking for Preference files that appear to have been changed around or after the time this issue started happening. You could try deleting (or moving) preference files out of your troubled user account to see if you can resolve the issue.

Does this issue happen when you use certain software or does it not matter what application you are typing into?

I'm assuming the latter.

You could also consider creating yet another test user account and then duplicating all your user library preferences from the troubled account into this new one and see if the problem appears in this new test account and then if it does. start deleting preference files one (or maybe a few) at a time until the problem goes away. To try to determine which file is corrupt.

You should also check for updates for all your installed third-party software as this could be related to bug in such software. Also if you could live without the third-party software for a while, try temporarily removing from your system. Sounds like you tried this to some degree. But knowing what software is causing the issue could help determine what preference files may need to be deleted/re-created.

You could use Activity Monitor (found in Applications/Utilities) to see what application processes are currently running. For some processes you can see what files and ports the process has open by viewing the detail information of that process.

Not necessarily, it could still be software or hardware.

Does you system seem taxed at all when this happens?

Does it happen with just one program or does it seem like it doesn't matter what program your in?

Try opening keyboard viewer and watching to see if it shows double hits when using the space bar. To open keyboard viewer: Open the Keyboard PreferencePane in System Preferences, goto the "Input Sources" tab and enable the "Show input menu in menu bar" checkbox, if it not already enabled. Then from the input menu select "Show Keyboard Viewer"

Also see it the you can get this issue to happen with another keyboard. If you can get another keyboard to show the issue then the problem is most likely software related. This in combination with it has happens in safe mode. Would make me lean towards reinstallation of the system software. Or to try booting from another drive with a fresh OS to test the hardware with.

No Problem, Good Luck hope it works out for you.

I still feel it a bad preference file. So I would try migrating to using a new user account or trying to determine which preference file is bad, Since this is keyboard related I would try tossing the preference file related to the keyboard and input sources. And only as a last resort would I break down and reinstall the OS.

Also when it failed in safe-mode which user account were you using?

If it was your original account it still could be a corrupt preference file in your user account that is causing this.

I'm having the exact same issue as OP- did you ever get this sorted out w/Apple?

TIA