Solution 1SYMBOLIC LINKS
Links that point to themselves can cause a recursive loop. Check the file system for directory links that link to itself. For example if /public_html/mydir points back topublic_html/ then that might create a recursive loop for PHP in which case you would need to filter public_html/mydir/.

To check for symbolic links go to Duplicator > Tools > General > Scan Validator > “Run Scan Integrity Validation”. This will find sym-links and unreadable files. When the scan iscomplete add the full path(s) of the “Symbolic Links” to the directory filter list on Step 1 of the package creation process.

If the scan validator does not pick up files then go into your host’s file manager and look for anything that would cause this (for instance that may look like /dir1 and if you gointo /dir1 it would contain the contents of / which would mean it would also include /dir1 etc). For these type of directories/links enable file filters and add the full directory pathsto the directories box when you are creating a package.

Note: If this process seems too technical then simply contact your host and ask them if there are any symbolic or recursive links in your WordPressdirectory structure. There are some instances where the scan validator might not pick a symbolic link on your server.

Solution 2LARGE FILE COUNTS
For some budget host setup with timeouts enabled; large file counts might cause the scan to timeout. If PHP or Apache timeouts are set to low and your trying to scan 250k+ filesthen the process may not be able to scan all the files.

To resolve goto Packages > Create New > Step 1 > Archive Directory filters and add a filter to the directory with the large file count. The recommend approach is to increase your PHP andWeb Servertimeouts so the scan is allowed time to finish.

Solution 3UNREADABLE FILES
On some systems certain utf8 characters can cause the scan to have issues. This is a very uncommon issue and typically more prevalent on Windowsoperating systems running lower version of PHP.

To check for unreadable files from within the plugin go to Duplicator > Tools > General > Scan Validator > “Run Scan Integrity Validation”This will run a scan check that will look for unreadable files. When the scan is complete add the path(s) of the “Unreadable Files” to the directory filter list on Step 1 of thepackage creation process.

Solution 4NO FILES FOUND
If you run a scan and the results show up with no files being found. In your server could be configured with “server separation”. You will need to contactyour hosting provider for more details however this can be an issue on some systems. Possible options in Domain Configuration window are:

1. No forwarding
2. Forward to subfolder without service separation
3. Forward to subfolder with service separation
4. Forward to IP/Host/URL

Switching temporarily to #2 will allow the Duplicator to run without issues for both the package and installer.

Solution 1A permission issue might be related to a file/directory or the .htaccess file. Try changing the permission of your hosts root .htaccess file to 755 and then try therequest a few times to see if it starts the scan. If the issue persists then try and contact your host.

Solution 2Check with your host for any mod_security rules which might be causing the issue and ask them to whitelist the rule causing the issue on your host.

Also see:
What can I do for issues with migrating a large site?
What can I try for 502/503/504 Gateway issues during the scan/build?
Recommended hosting providers for Duplicator?

Solution 3In some cases a poorly written plugin or theme could have code that conflicts with Duplicator. To resolve plugin/theme conflicts see Why is the Duplicator user interface (UI) not working?

Most 500 web server errors can be difficult to track-down as they are being thrown from the web server and not PHP. Below areseveral options you can try for 504 and 502 errors.

Solution 1Config Update
Consider the following updates to the .htaccess file.

Option 1: Change the dynamic value for ajax calls<IfModule mod_timeout.c>
<Files ~ ".php">
SetEnvIf Request_URI "admin-ajax" DynamicTimeout=240
</Files>
</IfModule>

Option 2: Update the .htaccess file from the file manager interface(Path: public_html/.htaccess) and also increased the max_execution_time limit from 300 to 3000from the Select PHP version interface provided in cPanel.<IfModule Litespeed>
RewriteEngine On
RewriteRule .* - [E=noabort:1, E=noconntimeout:1]
</IfModule>
Solution 2Cloudflare
If you’re using Cloudflare the below settings may help

1. Log in to Cloudflare
2. From Overview Page click “Advanced” > Click “Pause”
3. Run installer deployment
4. Turn Cloudflare back on

Solution 3Contact Hosting Provider
Connect with your hosting provider and let them know your getting a 500 error. Many times your host will have access to the web server logswhich can help isolate what is triggering the error on their server configurations. In some cases the host may be able to provide enoughinformation to give you a status as to why the 500 error is being thrown, this information in some cases can help us try different configurations inthe hosts environment.

Solution 4General Troubleshooting
There are several troubleshooting protocols you can implement to try and validate if the issue is indeed a networking issue between your browser and theserver. If you have the ability to try from a different computer or even different browser that can sometimes isolate the issue. For a fullrun-down of various ways to fix this issue please see this article onUnderstanding and Fixing 502 Bad Gateway Errors

Also see:
What can I try for 502/503/504 Gateway issues during the install?
Recommended hosting providers for Duplicator?

To resolve this issue please do the following:

1. Go to: WordPress-Admin > Duplicator Pro > Settings > Packages Tab > Advanced Settings
2. Change Thread Lock Type to “SQL”
3. Change JSON to “Custom”
4. Retry building a package

Solution 1Go to Packages > Create New > Check the “Archive Only the Database” checkbox. This will build only the database and let you know if thereis an issue with a specific file or directory. If the scanner completes then there is an issue with one of the files in your system. In this case you can follow these steps:

1. Go back to step one “1-Setup” and click the [root path] quick link to add the WordPress root directory as a filter then run the scanner.
2. If this works then continue adding and removing directories until you can locate the problem area. Start with the top-most directories and work your way down if notthen see “Test 2” below.

Solution 2If you try all the other options Issue A thru D above and it still fails then check your PHP error log and contact your hosting provider.