Backups recently began hanging at 0% after "Began backup"

I have this in my functions.php to cover that, which seemed to be working okay until recently:

if (!function_exists('gzopen')) {
function gzopen($filename , $mode, $use_include_path = 0 ) { return gzopen64($filename, $mode, $use_include_path); }
}

Where should I look for other PHP errors?

I’ve tried enabling debug mode in WordPress and sending that to a log file. I see some deprecation notices, but no errors when I trigger a backup. These are the deprecation notices I’m seeing for each request, if it’s relevant:

[16-Mar-2015 14:27:03 UTC] PHP Notice:  add_option was called with an argument that is <strong>deprecated</strong> since version 2.3 with no alternative available. in /var/sites/Encosia.com/public_html/blog/wp-includes/functions.php on line 3497
[16-Mar-2015 14:27:03 UTC] PHP Notice:  WP_User->id was called with an argument that is <strong>deprecated</strong> since version 2.1! Use <code>WP_User->ID</code> instead. in /var/sites/Encosia.com/public_html/blog/wp-includes/functions.php on line 3495
[16-Mar-2015 14:27:03 UTC] PHP Notice:  WP_User->id was called with an argument that is <strong>deprecated</strong> since version 2.1! Use <code>WP_User->ID</code> instead. in /var/sites/Encosia.com/public_html/blog/wp-includes/functions.php on line 3495
[16-Mar-2015 14:27:03 UTC] PHP Notice:  WP_User->id was called with an argument that is <strong>deprecated</strong> since version 2.1! Use <code>WP_User->ID</code> instead. in /var/sites/Encosia.com/public_html/blog/wp-includes/functions.php on line 3495
[16-Mar-2015 14:27:03 UTC] PHP Notice:  WP_User->id was called with an argument that is <strong>deprecated</strong> since version 2.1! Use <code>WP_User->ID</code> instead. in /var/sites/Encosia.com/public_html/blog/wp-includes/functions.php on line 3495
[16-Mar-2015 14:27:03 UTC] PHP Notice:  WP_User->id was called with an argument that is <strong>deprecated</strong> since version 2.1! Use <code>WP_User->ID</code> instead. in /var/sites/Encosia.com/public_html/blog/wp-includes/functions.php on line 3495
[16-Mar-2015 14:27:03 UTC] PHP Notice:  load_plugin_textdomain was called with an argument that is <strong>deprecated</strong> since version 2.7 with no alternative available. in /var/sites/Encosia.com/public_html/blog/wp-includes/functions.php on line 3497

I tried commenting that code out of functions.php and now I get this notice at the top of the UpdraftPlus debug tab:

Abort class-pclzip.php : Missing zlib extensions

After uncommenting that bit in functions.php, the zlib error is gone. So, it seems to be taking effect.

I’m looking everywhere I can for more errors, but all I can find in the PHP error log, apache error log, and the WordPress error log are those notices I posted above. After searching, it seems like those are probably coming from other plugins using older, deprecated APIs? Could those affect UpdraftPlus to this extent?

I wasn’t seeing a zlib error before in relation to this 0% stall. I was just testing to be sure the functions.php gzopen shim is still in effect by pulling it out, seeing that there’s a new error without it, putting it back, and verifying that the error is gone again.

I do have shell access to the server. It’s a VPS at Linode.

Interesting. Running it from the command line resulted in a full files/database backup without any errors. Going back to the wp-admin interface, backups still hang at 0%.

Interesting. When I disabled all plugins, trying to run a backup still had the same issue as before. However, I saw an error in the WordPress errors.log that I haven’t seen before:

[29-Mar-2015 02:31:56 UTC] PHP Fatal error: Cannot redeclare class UpdraftPlus_BinZip in /var/sites/Encosia.com/public_html/blog/wp-content/plugins/updraftplus/class-zip.php on line 12

Does that mean anything to you?