I had PS 1.75.2. I installed the 1-click upgrade 4.9.0 and ran the upgrade to 1.7.6.
After upgrade, the BO seemed fine but the FO is not working anymore. Error 500.
AH01071: Got error 'PHP message: PHP Fatal error: Uncaught InvalidArgumentException: "1.0E+15" cannot be interpreted as a number in /vendor/prestashop/decimal/src/Number.php:466\nStack trace:\n#0 /vendor/prestashop/decimal/src/Number.php(72): PrestaShop\\Decimal\\Number->initFromString('1.0E+15')\n#1 /src/Core/Localization/Number/Formatter.php(149): PrestaShop\\Decimal\\Number->__construct('1.0E+15')\n#2 /src/Core/Localization/Number/Formatter.php(106): PrestaShop\\PrestaShop\\Core\\Localization\\Number\\Formatter->prepareNumber(1.0E+15)\n#3/src/Core/Localization/Locale.php(155): PrestaShop\\PrestaShop\\Core\\Localization\\Number\\Formatter->format(1.0E+15, Object(PrestaShop\\PrestaShop\\Core\\Localization\\Specification\\Price))\n#4/classes/Tools.php(776): PrestaShop\\PrestaShop\\Core\\Localization\\Lo...\n'
At the same time, on another website, I did a clean install of PS 1.7.6 and everything works fine. So... is it a problem with the 1-click upgrade module or with the files it downloads before the upgrade?