Although I recently subscribed to Max through Roku, I find I cannot properly login into Max app on another device. When I try, the login goes through, but I’m asked to “resubscribe”.
Is that other device a Roku device? If so, is it linked to the same Roku account? If you're not sure, you can check what Roku account a device is linked to by checking the email address displayed under Settings->System->About on each device.
Yes it is. However, I had no idea that Roku TVs must share the same email address for apps to work. This is utterly ridiculous!
For apps to work? Apps will "work" no matter what account your device is linked to. However, subscriptions paid through Roku are tied to your Roku account. If you want to use a subscription on different devices (Roku or not) or on different Roku devices, bypass subscribing through a third party like Roku and subscribe directly with the provider.