If you ever get locked out of your own site as a result of Shield, for whatever reason, you can forcefully turn off all restrictions made by it.
How to use "forceoff" file to debug the problems
To do that, please follow the steps outlined below.
Step 1: Forcefully turn off all restrictions
Go to your FTP manager and create "forceoff" file by following the guide outlined in the article here.
This will act to temporarily disable the features of the plugin allowing you to get back in and change settings (debug the problems).
Important: Creating "forceoff" file will just temporarily disable processing of any security rules. It doesn't change any settings, it just doesn't enforce them.
Once you create it, please change the settings (debug the problem), and then remove the "forceoff" file.
Please note that, if you remove the file before changing settings, the problem will return.
Step 2: Examine the problems
Once you are back in, go to your Audit Trail logs to examine the problems.
Please see here how to review Audit Trail entries.
Step 3: Debug the problem
Now, you can debug / get the problems resolved.
Example 1: Problem caused by Firewall
When you go to your Audit Trail and you find the Firewall entries (what's triggering the block), go to Firewall module => Whitelist => and whitelist parameters that's getting blocked.
Please see here how to whitelist parameters.
Hint: If you have a problem to interpret the Firewall entries in your Audit Trail and you're not sure what parameter to whitelist, please read the article here.
Example 2: You got blacklisted
Go to IP Manager module and use its tool to remove yourself from the blacklist.
Please see here how to use IP Manager tool.
Reminder: You still should examine your Audit Trail to find out why you got blacklisted in order to get the problem resolved.
Example 3: You can't remember your access key
To get this kind of problem resloved, you don't need to examine Audit Trail (Step 2). You simply go to Security Admin module and enter/save a new access key.
For more information about this, please read the article here.
Example 4: When you try to login, you get 404 error
If you've renamed WordPress login page, the only way to access it is thorugh the new URL you have created. Otherwise, you'll get 404 error.
If you forget the new URL or for some reason it doesn't seem to work for you, simply go to the Login Guard module => Hide Login Page => remove the URL you have previously created => Save.
For more information about this, please read the article here.
Step 4: Remove "forceoff" file
Once you manage to debug the problem, go back to your FTP manager and remove the "forceoff" file.
Conclusion
Whenever you get locked out, the first step to take is to use the "forceoff" file.
Audit Trail always tells you what happened and what went wrong so you can debug the problem easily.