It should be showing you all your PHP errors in the log files. They intentionally never show to the screen, because that would create security problems.
But maybe something in your upgrade has damaged one or more of the bootstrap files that load before the debug logger is enabled, in which case you'll have to take much more drastic measures to find your problems:
Near the top of your /admin/includes/application_top.php file, you'll see this line:
Code:
define('DEBUG_AUTOLOAD', false);
Change that false to true, and add another line directly below it, as shown here:
Code:
define('DEBUG_AUTOLOAD', true);
define('STRICT_ERROR_REPORTING', true);
Now you should see all kinds of information, including errors and warnings and headers-already-sent messages, etc. Many of those messages will be a result of earlier messages, and thus not all information is actually indicative of an "error", so be careful not to send yourself on a wild goose chase.
What addons do you have installed?
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