If your flats have steel girder framing and/or concrete/breeze block walls and/or metal foil-backed plasterboard, then any and all have a considerable effects on WiFi in both a simple screening manner; and also from "Standing Waves" building up from reflections.
The usual WiFi radio frequency of 2.4 GHz has a Wave Length of about 12 Centimetres, so metallic objects of about that length, also 6 cms, 3 cms etc can have effects also, being directly related to that WiFi Wavelength, being half and quarter wave lengths.
Additionally, that radio frequency is readily absorbed by water, hence the magnetrons used in Microwave Cookers/Ovens operate on that frequency, relying on that particular effect - along with other items such as baby alarms.
Your body is largely water, so as you move, it will absorb some of the WiFi signal in degree, as will other human occupants, pets, even foodstuffs outside of metallic objects such as refrigerators, freezers etc.
If your WiFi source is tucked away in a corner "to be tidy" or simply out-of-the-way, the corner structure, particularly the metal foil on the back of plasterboard may be acting like a "Corner Reflector", such as you may see around airfields and harbours, for obstructions or as lane markers, thus beaming your WiFi in a limited direction, rather than the wide general coverage you want.
One way to get some idea of how WiFi radiates is to place a low level light source such as a small single LED of the older variety, at your WiFi source. Or your Router probably already has one working.
Then when it is dark with most/all other lighting off, observe how that LED light spreads through your flat, bearing in mind that it is not a perfect analogy.
Note the differences as others move about the rooms, mirrors reflecting and concentrating it in some places, whilst less/none gets beyond the mirror.
Open and close doors.
Bluetooth is similar.
The knocked-down flats are unlikely to have had any effect, unless extremely close, "just outside your window" etc. The degree that you can detect other WiFi circuits in your own block might give you some idea.
In other words, it is miraculous that WiFi works!
In degree, this general absorption is useful in that it very much reduces the spread of YOUR WiFi signal beyond your immediate environment, so minimising the chances of others using it without your knowledge.
(Yes, in particular circumstances with modified aerials etc, it can be used for line-of-sight etc - but the vast majority of WiFi users will not indulge in such practices.)