When upgrading we always needs to add a JSON header to sp-startup/install/sp-upgrade.php (around line 40). Can you please add a line permanent? The sent header is wrong.
header(‘Content-type: application/json;’);
header(‘Content-type: application/json; charset=’ . SFCHARSET); // if SFCHARSET is in scope
header(‘Content-type: application/json; charset=’ . SFCHARSET); // if SFCHARSET is in scope