"undefined"
Are you certain that value is coming from Companies House, and is not e.g. because you’re asking for something that doesn’t exist in a data structure?
Apologies if this is something you’re already aware of but there are effectively a “zoo” of rather different types of organisations / entities in the Companies House data set. The vast majority are “companies” but there are a range of different types of entity in it (you’d have to ask Companies House / consult law and “policy” as to why exactly). Some of these have minimal information, or different information that “companies” usually have available. The main “registrar” for those is not Companies House but another organisation (e.g. relevant charities body) - in some cases this is indicated by a field in the Company Profile.
The main one I can think of now which could give you “undefined” because it doesn’t return that field is:
Charities: e.g. /company/CE013477 (Scottish charities start with CS) - these do not return a status. (Note the main registrar / regulator for these varies - The Charity Commission in England and Wales, OSCR in Scotland, The Charity Commission for Northern Ireland there.)
You can obtain examples / investigate using the Advanced Search e.g. via the website (or API):
"Lifecycles"
I believe Companies House has a short guide (albeit aimed more at company officers but may be useful?):
(First part relates to accounts rather than status changes)
… And you can also search this forum and find specific information.
Good luck.