Hello,
So, to sum up : 1 Click Upgrade didn't work and I tried to update my website from 1.7.4.4 to 1.7.5 (using on PHP 7.2) by following closely the instructions given here (https://devdocs.prestashop.com/1.7/basics/keeping-up-to-date/upgrade/) which of course didn't work, following Murphy's law.
So all I got was a blank page, I couldn't even use the upgrade database tool. So I headed back to my previous version which I had backuped, obviously, but after having reuploaded it - blank page........
Derp.
After setting "define('_PS_MODE_DEV_', true)", all I got was this, and...... HELP. Please..
Whoops, looks like something went wrong.
(1/1) RuntimeException
The autoloader expected class "Defuse\Crypto\RuntimeTests" to be defined in file "/home/users3/k/krisg/www/steelwork2019/vendor/composer/../defuse/php-encryption/src/RuntimeTests.php". The file was found but the class was not in it, the class name or namespace probably has a typo.
in DebugClassLoader.php line 205
at DebugClassLoader->checkClass('Defuse\\Crypto\\RuntimeTests', '/home/users3/k/krisg/www/steelwork2019/vendor/composer/../defuse/php-encryption/src/RuntimeTests.php')in DebugClassLoader.php line 158
at DebugClassLoader->loadClass('Defuse\\Crypto\\RuntimeTests')
at spl_autoload_call('Defuse\\Crypto\\RuntimeTests')in Crypto.php line 178
at Crypto::encryptInternal('date_add|2019-01-31 22:29:35¤id_lang|1¤id_currency|1¤checksum|1130431320', object(KeyOrPassword), false)in Crypto.php line 25
at Crypto::encrypt('date_add|2019-01-31 22:29:35¤id_lang|1¤id_currency|1¤checksum|1130431320', object(Key))in PhpEncryptionEngine.php line 58
at PhpEncryptionEngineCore->encrypt('date_add|2019-01-31 22:29:35¤id_lang|1¤id_currency|1¤checksum|1130431320')in PhpEncryption.php line 59
at PhpEncryptionCore->encrypt('date_add|2019-01-31 22:29:35¤id_lang|1¤id_currency|1¤checksum|1130431320')in Cookie.php line 362
at CookieCore->encryptAndSetCookie('date_add|2019-01-31 22:29:35¤id_lang|1¤id_currency|1¤checksum|1130431320')in Cookie.php line 400
at CookieCore->write()in FrontController.php line 670
at FrontControllerCore->smartyOutputContent('errors/maintenance.tpl')in FrontController.php line 729
at FrontControllerCore->displayMaintenancePage()in FrontController.php line 469
at FrontControllerCore->init()in Controller.php line 236
at ControllerCore->run()in Dispatcher.php line 428
at DispatcherCore->dispatch()in index.php line 28