I'm using Joomla version 3.9.6. I encountered a problem just after a windows update. The error displayed is:
Warning: session_start(): Failed to read session data: user (path: C:\xampp\tmp) in C:\xampp\htdocs\joomla3.96\libraries\joomla\session\handler\native.php on line 260
Error: Failed to start application: Failed to start the session