Hi Ehab,
I have seen where water will run underneath floor tiling and wick upwards at the edges. As others mentioned, thermal imaging pictures would help with the pattern recognition of where the materials are cooler. Moisture meter readings are helpful, especially as the saturation level changes laterally - it can be a rudimentary direction finder. Vertically it tends to saturate near the bottom, but it can definitely trickle down in one specific location and splay outwards. Personally I would not rule out a plumbing leak, it could be anything. Water can travel down two or three stories from the roof and then go inwards. AC units on the roof? AC venting? Not really enough information.
I all ways try to read what the problem is communicating.
Personally I would be checking in the apartment ceiling directly below and also the apartment floor directly above and the exterior. It is in those apartment owners best interest to get this remedied.
If it’s a larger tower building this may be a replicated deficiency pattern. Towers are blocks built upon other blocks… so a problem in one area could be repeated elsewhere.
What were the results from the thermal imaging of all walls, ceilings, floors?
