I found this error repeated several times for two of the pages on my website.
Warning: Cannot modify header information - headers already sent by (output started at /home/customer/www/mydomain.com/public_html/includes/common.inc:2800) in user_cookie_save() (line 4041 of /home/customer/www/mydomain.com/public_html/modules/user/user.module).
I checked a bit around and found other similar errors with "Headers already sent" but none of them on the user_cookie_save function.
How can I debug fix it?
I'm running on Drupal 7.78, PHP 184.108.40.206 and as modules that could influence the cookies, I'm running just the EU Cookie compliance module.
What I find strange, is that I do not recall having seen this error before. There is a small chance that the error was there ad I did not see it because the logs are filled with page not found, and access denied errors by nice persons from the internet :) I would say though that that is a small chance as I've checked many times the logs in the past and did not see this error.
I have no idea what changed, and also no idea of what is the impact of this error, it's a warning, but I can't reproduce it.