Hi @unai
Could you please check your database if the saved values have the weird encoding too? If they are, could you please check the collation of the tables. I believe the right collation should be “utf8mb4_unicode_ci”.
It’s possible that your PHP7 had a setup that changes the encoding. The best way would be asking your hosting about it. Also, please backup your website first before you change your server setup.
Thanks!