The problem went away when I installed the phpmyadmin storage database. But still, this error is confusing and I think it should not appear on a fresh installation.

Can you please look to web server error logs to see what has caused the error?

I probably found where the problem is, but still having that confirmed would be nice...

Looks like phpMyAdmin has taken over the logging. I don't see any errors in my syslog (which php is configured to log by default).

phpMyAdmin does not configure this, so it's most likely the PHP is not configured to do so (eg. if using fpm, you need to enable catch_workers_output to get useful logging from PHP).

@nijel I added catch_workers_output to fpm, and it started giving me extra logs from my other systems. But none from phpMyAdmin.

I just upgraded to 4.7.0 and still see the dreaded error. Sometimes I get a "token mismatch" error.

I suppose that 500 Internal Server Error is coming from phpMyAdmin itself and not fpm.

Is it possible?

No, phpMyAdmin AFAIK does not return 500 on it's own, so it has to come from PHP or web server...

@nijel guess what? phpMyAdmin does return 500 errors on it's own.

I managed to debug the XHR request and here's what I got:

<h1>phpMyAdmin - Error</h1>
<p>Error during session start; please check your PHP and/or webserver log file and configure your PHP installation properly. Also ensure that cookies are enabled in your browser.<br /><br />session_start(): Failed to decode session object. Session has been destroyed</p>

@nijel that means that phpMyAdmin takes over the errors and they don't hit my regular logging system. And the biggest problem is that if an error happens during an ajax request, there is no way of finding out which error it is without using special tools to check the reply.

I think this is a major problem that needs to be looked into.

Indeed it should properly report json in this case.

This seems to be caused by fix for #12810...