Error After Updating - Warning: Session_Name(): Cannot Change Session Name When Headers Already Sent In

Hello

Recently been updating one of the websites (not sure to what version exactly) and now getting the errors below. I can't login to the back end either, just reloads the page. I've tried the usual stuff, cleared the var/cache. Does anyone have any ideas please?

Using PHP Ver 7.4

Warning: session_name(): Cannot change session name when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 246

Warning: session_id(): Cannot change session id when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 258

Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /home4/northing/public_html/app/Tygh/Web/Session.php on line 400

Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /home4/northing/public_html/app/Tygh/Web/Session.php on line 401

Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /home4/northing/public_html/app/Tygh/Web/Session.php on line 402

Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /home4/northing/public_html/app/Tygh/Web/Session.php on line 403

Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /home4/northing/public_html/app/Tygh/Web/Session.php on line 404

Warning: session_cache_limiter(): Cannot change cache limiter when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 406

Warning: session_cache_expire(): Cannot change cache expire when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 407

Warning: session_set_cookie_params(): Cannot change session cookie parameters when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 425

Warning: session_set_save_handler(): Cannot change save handler when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 443

Warning: session_start(): Cannot start session when headers already sent in /home4/northing/public_html/app/Tygh/Web/Session.php on line 340