Hi guys,
PHP 7.4.33 + MariaDB 10.5.15 + Joomla 4.2.6 (Upgraded from 3.10.11) + some Extensions (including Seblod)
I was managing users and it seems like that after a session expiration I had suddenly back this Error 500 I'm reporting.
I'm going to try to replicate the Error, so, the question is:
Do you have any idea what could be causing it?
Do you have any ideas on what I have to be careful about?

Warning: session_start(): Failed to initialize storage module: user (path: /tmp) in /home/…/libraries/vendor/joomla/session/src/Storage/NativeStorage.php on line 478

Warning: mysqli::real_escape_string(): invalid object or resource mysqli in /home/…/libraries/vendor/joomla/database/src/Mysqli/MysqliDriver.php on line 388

Warning: mysqli::real_escape_string(): invalid object or resource mysqli in /home/…/libraries/vendor/joomla/database/src/Mysqli/MysqliDriver.php on line 388

Warning: mysqli::prepare(): invalid object or resource mysqli in /home/…/libraries/vendor/joomla/database/src/Mysqli/MysqliStatement.php on line 137

Host 'localhost' is not allowed to connect to this MariaDB server

Joomla\Database\Exception
PrepareStatementFailureException

in /home/…/libraries/vendor/joomla/database/src/Mysqli/MysqliStatement.php (line 141)
in /home/…/libraries/vendor/joomla/database/src/Mysqli/MysqliDriver.php -> __construct (line 1048)
in /home/…/libraries/vendor/joomla/database/src/DatabaseDriver.php -> prepareStatement (line 1900)
DatabaseDriver->setQuery(object(MysqliQuery))
in /home/…/administrator/components/com_templates/src/Model/StyleModel.php (line 737)
StyleModel->getAdminTemplate(0)
in /home/…libraries/src/Application/AdministratorApplication.php (line 230)
AdministratorApplication->getTemplate(true)
in /home/…/libraries/src/Error/Renderer/HtmlRenderer.php (line 50)
HtmlRenderer->render(object(ConnectionFailureException))
in /home/…/libraries/src/Exception/ExceptionHandler.php (line 121)
ExceptionHandler::render(object(ConnectionFailureException))
in /home/…/libraries/src/Exception/ExceptionHandler.php (line 72)
ExceptionHandler::handleException(object(ConnectionFailureException))
in /home/…/libraries/src/Application/CMSApplication.php (line 323)
CMSApplication->execute()
in /home/…/develop/administrator/includes/app.php (line 61)
require_once('/home/…/administrator/includes/app.php')
in /home/…/administrator/index.php (line 32)

Joomla\Database\Exception
ConnectionFailureException

Could not connect to database: Host 'localhost' is not allowed to connect to this MariaDB server
in /home/…/libraries/vendor/joomla/database/src/Mysqli/MysqliDriver.php (line 280)
in /home/…/libraries/vendor/joomla/session/src/Handler/DatabaseHandler.php -> connect (line 233)
DatabaseHandler->open('/tmp', '051771ea6d83c9739ce0c61412d04d6a')
in /home/…/libraries/vendor/joomla/session/src/Storage/NativeStorage.php session_start (line 478)
NativeStorage->start()
in /home/…/libraries/src/Session/Storage/JoomlaStorage.php (line 295)
in /home/…/libraries/vendor/joomla/session/src/Session.php -> start (line 406)
in /home/…/libraries/vendor/joomla/session/src/Session.php -> start (line 333)
Session->has('registry')
in /home/…/libraries/src/Session/Session.php (line 191)
Session->get('registry')
in /home/…/libraries/src/Application/CMSApplication.php (line 656)
CMSApplication->getUserState('application.lang')
in /home/…/libraries/src/Application/AdministratorApplication.php (line 162)
AdministratorApplication->doExecute()
in /home/…/develop/libraries/src/Application/CMSApplication.php (line 294)
CMSApplication->execute()
in /home/…/administrator/includes/app.php (line 61)
require_once('/home/…/administrator/includes/app.php')
in /home/…/administrator/index.php (line 32)