Add a plugin like Kint Debugger + Debug Bar and add the following code to your functions.php.
global $wp;
ob_start('kint_debug_ob');
d($wp);
ob_end_flush();
When you check the Debug Bar you should see the backtrace which will tell you which order functions were fired in. Loading 8 times is quite high for a single request.
There is also a backtrace function you can use that is less detailed if you don’t want to go the plugin route – wp_debug_backtrace_summary.
echo "<!----- BACKTRACE / START ----->";
print_r ( wp_debug_backtrace_summary() );
echo "<!----- BACKTRACE / END ----->";
It is a bit odd to just have a random wp_insert_post in your functions.php so perhaps wrapping your logic in a hook like init could help in the mean time.
There is also a possibility this is not just a single request. heartbeats will ping the backend if you’re in the admin section and It’s possible wp-cron can trigger it to load as well (but I’m not sure).
To double check it all, enable WP_DEBUG_LOG and log the events.