Shopware 5.0.0 is not compatible with php7.1.
You need to make the update with php7.0 (e.g. in a local environment). Perhaps you can try the manual update package: https://de.shopware.com/download
Shopware 5 - Update Guides - Updating Shopware
Shopware 5.0.0 is not compatible with php7.1.
You need to make the update with php7.0 (e.g. in a local environment). Perhaps you can try the manual update package: https://de.shopware.com/download
Shopware 5 - Update Guides - Updating Shopware