After a long while, I took another look at the error_log.
The errors disappeared when I added Layout MIN and MAX width numbers into the Style and Configure Layout Options.
When I removed the numbers and saved, the errors returned. So the issue appears to be that blank MIN/MAX Width layout options will produce these error messages for some reason.
Also, I did not mention this earlier but it seems like it could be relevant. There is one more error -- a PHP Warning -- that shows up just before the other errors I mentioned before.
Code:
[17-Dec-2019 10:50:20 UTC] PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback, no array or string given in /.../wp-includes/class-wp-hook.php on line 288 [17-Dec-2019 10:50:20 UTC] PHP Warning: A non-numeric value encountered in /.../wp-content/themes/atahualpa/css.php on line 137 [17-Dec-2019 10:50:20 UTC] PHP Warning: A non-numeric value encountered in /.../wp-content/themes/atahualpa/css.php on line 138
Code:
[17-Dec-2019 11:15:17 UTC] PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback, no array or string given in /.../wp-includes/class-wp-hook.php on line 288 [17-Dec-2019 11:15:19 UTC] PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback, no array or string given in /.../wp-includes/class-wp-hook.php on line 288 [17-Dec-2019 11:15:27 UTC] PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback, no array or string given in /.../wp-includes/class-wp-hook.php on line 288
