Topic
Fixes for the errors that take a WordPress site down.
Troubleshooting
The REST server ran and found no registered route that matches both the path and the HTTP method. Either the route was never registered for this request, the URL does not match its pattern, or the method is wrong — and the message is the same for all three.
Troubleshooting
The script ran before jQuery existed on the page, or on a page where nothing asked WordPress to load jQuery at all. The fix is to declare the dependency, not to add another copy of the library.
Troubleshooting
A redirect loop is two rules that disagree about the correct URL, each sending the browser to the other's answer. Trace the hops with curl, and the two Location headers tell you which layers are fighting: proxy, server, WordPress or a plugin.
Troubleshooting
The log line names the missing table and the code that asked for it. A core table, a plugin's table and a table with the wrong prefix are three different problems, and only one of them is fixed by reactivating a plugin.
Troubleshooting
When the error says the arguments were passed in class-wp-hook.php, WordPress called your function with fewer values than it declares. The cause is nearly always the fourth parameter of add_action or add_filter, which defaults to one.
Troubleshooting
PHP 8.2 started warning whenever code assigns a property a class never declared. The site keeps working. The notice tells you which plugin or theme has not been updated for modern PHP, and you see it only because debugging is switched on.
Troubleshooting
PHP refused to compile a file, so nothing in it ran. The message names the file and a line, but the line is where PHP gave up, which is often one line after the actual mistake. Here is how to read it and get the site back without the dashboard.
Troubleshooting
WordPress counts the characters a plugin printed while it was being activated but never shows you what they were. The count alone narrows it down, and a few lines in a must-use plugin show you the rest.
Troubleshooting
The error names PclZip, but PclZip is only the last of two unzippers to give up. By the time you read it, ZipArchive has already rejected the file too — so the archive is truncated or not a ZIP at all, and the fix is to find out what was actually downloaded.
Troubleshooting
"Download failed." is a wrapper. WordPress appends the real reason after it — a status message, a cURL error, a temp-folder problem — and each one points somewhere different: the vendor, the network, or your own server.
Troubleshooting
Error 60 means the remote server presented a certificate and WordPress refused to trust it. WordPress checks against its own bundled list of authorities, not the server's, which is why the browser can be happy while the site is not.
Troubleshooting
The image was uploaded and saved; the server died while making the smaller copies of it. WordPress retries five times and then deletes the attachment, which is why the photo vanishes from the library after the error.