1. When uploading an image in WordPress, it prompts: The server cannot process the image. This happens if the server is busy or does not have enough resources to complete the task. Uploading a smaller image may help. The suggested maximum size is 2560 pixels. See Figure 1.
2. Checked the uploaded image size, which is 23 KB, confirming it is not caused by the image being too large. See Figure 2.
3. Decided to open the preview with photo software, then take a screenshot and save it to overwrite the original image. See Figure 3.
4. Uploaded again, but it still failed.
5. To debug in WordPress, refer to: https://wordpress.org/support/article/debugging-in-wordpress/ . Edit wp-config.php
/**
* 开发者专用：WordPress 调试模式。
*
* 将这个值改为“true”，WordPress 将显示所有用于开发的提示。
* 强烈建议插件开发者在开发环境中启用本功能。
*/
define('WP_DEBUG', true);
6. Refreshed the page, and there are some prompts. See Figure 4.
Warning: Use of undefined constant wp_cumulus_widget - assumed 'wp_cumulus_widget' (this will throw an Error in a future version of PHP) in /data/wwwroot/www.shuijingwanwq.com/wp-content/plugins/wp-cumulus/wp-cumulus.php on line 375
Deprecated: Function register_sidebar_widget is deprecated since version 2.8.0! Use wp_register_sidebar_widget() instead. in /data/wwwroot/www.shuijingwanwq.com/wp-includes/functions.php on line 5383
Deprecated: Function register_widget_control is deprecated since version 2.8.0! Use wp_register_widget_control() instead. in /data/wwwroot/www.shuijingwanwq.com/wp-includes/functions.php on line 5383
Deprecated: Since version 2.0.0! The argument used when calling the function has_cap is deprecated! User levels are deprecated, please use capabilities instead. in /data/wwwroot/www.shuijingwanwq.com/wp-includes/functions.php on line 5667
6. Uploaded again, and surprisingly, the upload succeeded. This was just after enabling debug. See Figure 5.
7. Reverted the changes in step 5. Uploaded again, and the upload succeeded. It feels like a temporary server-side issue. I have decided to stop looking into it for now.