wp-admin/error_log contains warnings

My WordPress wp-admin folder contains an error_log file that shows multiple warnings for the following:

[13-Oct-2021 01:43:20 UTC] PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘_return_false’ not found or invalid function name in /public_html/wp-includes/class-wp-hook.php on line 303

It says that the function that is missing is called ‘_return_false’. Of course this should be __return_false (2 underscores), however when I do a grep on the entire WordPress folder, I find no matches for ‘_return_false’ other than those in the error_log file.

I did the following command: grep -R “_return_false” * | grep -v “__return_false”

How can I determine what plugin or function is the cause of the warning and how do I resolve it?