Is using the same Redis instance for different applications against Separation of Concerns principle?

I have an application A which is strictly working together with application B. They're kind of pieces of a bundle.

Currently they are interacting between each other via HTTP calls. When app A needs something, it sends an HTTP API call to app B. But since HTTP is much more slower than Redis calls, I consider to change my flow as using Redis set/gets instead of HTTP calls.

No any other applications needs to have same relationship as A and B do.

So, is using Redis to share data between two applications instead of API calls against separation of concerns principle or not?