Uncaught Error: Class ‘Redis’ errors on a site I’ve transfered to new hosting

The file wp-content/object-cache.php is one of the dropins – PHP files with custom code that are not plugins. It is used when you are using a persistent object cache plugin, and it will be loaded automatically.

Normally the plugin will create that file. But if you move all the files without the plugin, the code in that file doesn’t work anymore, and you get your error message.

So you either have to delete the file, or install the plugin again. In this case probably the Redis Object Cache plugin.