How should I interpret Foreign, Commonwealth & Development Office advice?

The Foreign, Commonwealth & Development Office (FCDO) gives advice to travellers. CSP travel insurance will not cover you if you travel to a country/part of a country which the FCDO advise against all travel

If the FCDO advise against all but essential travel to a country or part of a country, we will cover Business Trips to such locations but not Leisure Trips.

You should check the status of any country you intend to visit and wish to be covered in.  The FCDO gives country specific advice at its website https://www.gov.uk/foreign-travel-advice.