Hi, just to share my view...

Most likely the crack is structure crack, suspected due to under provide of steel reinforcement.

I suggest you to ask your neighbour if they have the same problem. If it happens to all unit at the same location. High percentage there are problem with the design and you should inform the developer for rectification/varification.

If you happen know someone who is engineer and if you manage to bought the structure plan of your unit, can ask them for help and give you their professional view.

Once the root cause identified. the rectification would be simple.
Hope it helps