Based on the replies, it seems the problems were fixed, but just to comment on what was discussed above.
If the file is completely blank, then there's likely a PHP error which might not be logged to the Flarum log file, but should be logged in the global system PHP error file (might be the Apache error file on Apache)
However if it contains 3-4 entries it's entirely normal. It's an index to the other files. Even if you have few records, everything is now always split like for large forums.
The /sitemap-live/<number> subfolder is basically a virtual folder that returns each file that would be created by the cached mode. As the "live" part indicates, they aren't actually cached when accessed that way but instead generated on the fly.
Hari This setting is missing! [...] forgot to remove the below code from extend.php
The setting and the line in extend.php achieve the exact same thing. Both are fully supported options.
The choice was made to hide the setting in the admin when the extender is used, otherwise it would be confusing on a shared hosting where the host made the choice to force that value for the client, since you can't re-enable a resource that was disabled from extend.php.
