Warning: Cannot modify header information (class-jwt-auth-public.php on line 94)

Hello support team,

Currently, our WordPress-WooCommerce site is using the “JWT Authentication for WP REST API” plugin to synchronise our products from our ERP System to WooCommerce. Since at least 16th March 2021 we are facing extreme long loading times which lead to timeout errors. This prevents the synchronization to work properly.

We don’t know whether the following warning (which is originated in the plugin JWT Authentication for WP REST API) could have something to do with the timeout errors:

Warning: Cannot modify header information - headers already sent by (output started at /home/revendot/public_html/revendoch/wp-includes/functions.php:4757) in /home/revendot/public_html/revendoch/wp-content/plugins/jwt-authentication-for-wp-rest-api/public/class-jwt-auth-public.php on line 94

The last version of the plugin JWT Authentication for WP REST API: 1.2.6 and last version of WordPress: 5.7.1 is being used.
We have also tested with both the last version of WooCommerce (5.2.2) and the previous version (5.2.1) without success (same timeout errors).

We would be very grateful if you could have a look at the file (class-jwt-auth-public.php line 94) and publish a fix to the issue soon.

In parallel to this, since 8th December 2020 we are facing multiple PHP fatal errors which seem to have been recorded into the error_log file:

[08-Dec-2020 10:03:12 UTC] PHP Fatal error:  Maximum execution time of 30 seconds exceeded in /home/revendot/public_html/revendoch/wp-content/plugins/woocommerce/includes/class-wc-product-attribute.php on line 270
[08-Dec-2020 10:04:18 UTC] PHP Fatal error:  Maximum execution time of 30 seconds exceeded in /home/revendot/public_html/revendoch/wp-content/plugins/woocommerce/includes/wc-core-functions.php on line 1713
[08-Dec-2020 10:05:15 UTC] PHP Fatal error:  Maximum execution time of 30 seconds exceeded in /home/revendot/public_html/revendoch/wp-includes/class-wp-hook.php on line 286
[08-Dec-2020 10:07:17 UTC] PHP Fatal error:  Maximum execution time of 30 seconds exceeded in /home/revendot/public_html/revendoch/wp-includes/class-wp-term.php on line 197
[08-Dec-2020 10:08:15 UTC] PHP Fatal error:  Maximum execution time of 30 seconds exceeded in /home/revendot/public_html/revendoch/wp-includes/option.php on line 94

…

[22-Apr-2021 08:57:26 UTC] PHP Fatal error:  Maximum execution time of 30 seconds exceeded in /home/revendot/public_html/revendoch/wp-includes/functions.php on line 642
[22-Apr-2021 08:59:11 UTC] PHP Fatal error:  Maximum execution time of 30 seconds exceeded in /home/revendot/public_html/revendoch/wp-content/plugins/woocommerce/includes/data-stores/class-wc-product-data-store-cpt.php on line 364
[22-Apr-2021 09:00:17 UTC] PHP Fatal error:  Maximum execution time of 30 seconds exceeded in /home/revendot/public_html/revendoch/wp-includes/class-wp-term.php on line 197
[22-Apr-2021 09:01:13 UTC] PHP Fatal error:  Maximum execution time of 30 seconds exceeded in /home/revendot/public_html/revendoch/wp-content/plugins/woocommerce/includes/class-wc-product-attribute.php on line 194
[22-Apr-2021 09:02:21 UTC] PHP Fatal error:  Maximum execution time of 30 seconds exceeded in /home/revendot/public_html/revendoch/wp-includes/class-wp-hook.php on line 283
[22-Apr-2021 09:05:13 UTC] PHP Fatal error:  Maximum execution time of 30 seconds exceeded in /home/revendot/public_html/revendoch/wp-content/plugins/woocommerce/includes/abstracts/abstract-wc-data.php on line 836
[22-Apr-2021 09:06:11 UTC] PHP Fatal error:  Maximum execution time of 30 seconds exceeded in /home/revendot/public_html/revendoch/wp-includes/formatting.php on line 2237

This error occurred every single minute since 8th Dec. 2020 until we decided to set the maximum execution time to 300 seconds on 22nd April 2021. Since that change, the error has not occurred any more (or at least hast not been logged)
Nevertheless, the Synchronization via your plugin (JWT Auth WP REST API) still does not work as expected.

Any further advice on the matter would be appreciated.

Best regards.