Hi all,
I too have a problem while updating from J3.7.5 to 3.8.
The update stalled, and now I am unable to see the site or log in. When I go to the site I get this:
500 - Application Instantiation Error

Below is the message I get after setting error_reporting to 'maximum. Hopefully displaying this might prompt someone to help me restore the site.

Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; plgSystemK2 has a deprecated constructor in /home/xxxxx/public_html/plugins/system/k2/k2.php on line 15

Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; plgSystemPiwik has a deprecated constructor in /home/xxxxx/public_html/plugins/system/piwik/piwik.php on line 10

Is there a fix for the k2 part of this message?
Hope someone can help as I need to get the site up as soon as possible.
Thanks, Nick

Hello,

A Deprecated notice will not affect your site's functionality in any way.
Look in your error_log for any Fatal errors.