Error after restore: Failed to start session

[wetken]

I had exactly this issue today, but it was preceded by an 'unable to create directory' message, and the update stalled. I then got the 500 error after trying to use the site. I resolved it by doing a complete restore to the pre-update state, executing chown -R to ensure there were no files not owned by the site, then re-starting the update. However, I now have an error which I had thought was fixed;

Warning: ini_set(): A session is active. You cannot change the session module's ini settings at this time in /home/<myuser>/public_html/<mysite>/libraries/joomla/session/handler/joomla.php on line 48

Warning: Cannot modify header information - headers already sent by (output started at /home/<myuser>/public_html/<mysite>/libraries/joomla/session/handler/joomla.php:48) in /home/<myuser>/public_html/<mysite>/libraries/joomla/session/handler/joomla.php on line 110
Error displaying the error page: Application Instantiation Error: Failed to start the session because headers have already been sent by "/home/<myuser>/public_html/<mysite>/libraries/joomla/session/handler/joomla.php" at line 48.

There was a patch for this; do I need to re-apply it?

[wetken]

Moderator: you have split this off from another post which gave it context but not labelled it appropriately. The 500 error was following an update from 3.7.5 to 3.8; the restore was my way of recovering, not the cause of the error.
As regards the Instantiation error, commenting out line 48 in joomla.php allows the application to run, apparently successfully, but time will tell, I guess.
A better title might have been 'Error 500 - Instantiation Error following update from 3.7.5 to 3.8'