As you haven't mentioned FTTC, what does the information on the checker say about the type of connection available to other properties which can get Infinity? i.e. FTTC or FTTP?
If you are in an FTTP area and your building is now divided into flats, that can cause issues with wayleaves regarding installing FTTP equipment into communal areas of the building. It may be easier to side-step that problem if you are in an overhead-fed FTTP area (as opposed to underground-fed) as it may sometimes be easier to supply individual flats that way.