The error message is mentioning
Unable to retrieve converted schema, which leave me to believe you have indeed edited the Schema (or one of its embedded Schemas) after it was initially created, and while there was already one or more Components created based on it. While this is possible, it can sometimes cause the system to jump into an error mode it cannot recover itself from.
When Component content is out of sync with the Schema, the UI tries to update the Component and match it with the Schema. Typical things it can fix are removing elements from the Component XML if those fields have been removed from the Schema, and reordering elements in the Component XML when the order of those fields in the Schema have changed.
Apparently harder topics for the UI to fix are changes of the Schema namespace and changes to Embedded Schemas (they are in the namespace of the parent Schema). I've seen it happen before that on what looked like a simple change, the system tried to fix it, but got stuck. I have a feeling a similar thing happened in your case.
So much for my assessment of your problem, on to the solution, I'm afraid the best thing I can suggest you is to contact SDL Customer Support directly and ask for their help. Since this might require a bit more than just telling you what to do, and it might also be an indication of a defect in the system (perhaps there are already hotfixes available for your issue).
As for the other part of your question; "is it good practice to assign unique namespaces per Schema?".
The answer to this is: Yes. It is best practice to assign each Schema its own unique namespace, this is also what automatically is done when you create a new Schema. The reason for this is that a Schema defines a structure for XML content, and in there you could define a field
Name. Now the field
Name of a Schema
Book, might have a different meaning that the field
Name of the Schema
Person, hence those Schemas should have a unique namespace.
It is okay if you want to change the standard assigned uuid into a more readable namespace, but it is best practice to do this while you create the Schema and before you create any content based on it. Changing a Schema after it has been created is never something you should think lightly of, always be aware of what change you are making and think if it is really necessary.