Problems with last Update (4.9) class-wp-hook.php

Hello.

I updated my wordpress version to 4.9.4 and now i have this warning on my woocommerce checkout pages:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘my_checkout_msg’ not found or invalid function name in /home/emprendiendo/public_html/escuela/wp-includes/class-wp-hook.php on line 286

1. All my plugins are updated
2. I already deactivated one by one the plugins to be sure if one of them was having troubles and i still get this warning
3. The checkout page is working, but imagine to see a warning before you pay for a product…I need to fix this.

I don’t know what else can do to fix the problem.

Can anybody help me?

Thanks a lot

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