Damp corner - What is the reason?

which year was the new building constructed (in Havana the old town is 400 years and the new town is 200 years old), was the new building constructed by a company or DIY, was waterproofing done on the floor slab, basement, exterior walls, base? That could be a construction defect and it must be fixed

Is the current state shown in image 2 of how the downpipe is connected to the drain pipe?

If yes, then I would say that the elbow is installed the wrong way around. Here, the rainwater can freely escape if it backs up in the rest of the pipe. It is possible that the pipes of the remaining line are also installed the wrong way around. Thus, water can also escape at the connection points if, for example, the rubber seals are not properly seated or are completely missing.

In heavy rain, downpipes can become pressure pipes if the drainage system fails.