hi sir , im not a freelancer , im a profesional web developer with 5 years of web developement , i had worked before with Deco Evo theme , i know many issue in this theme such the multi-shop errors and much mores , for your problem i know that the smarty templates haad errors of compatilbity that's why and same modules in your prestashop must be upgraded , and if you have also some classess or controllers overrides like agile paypal .. it's maybe cause problems because the new Prestashop php functions are changed
i have a lot of experience with prestashop and i rady to resolve your problem and recover your broken website :)
im availble at any time to resolve this issue and immediatly
Best regards