It would appear your service is from a Satellite system.
The title of the thread says "TDT" - which is the Spanish TV system - Television Digital Terrestrial - Terrestrial meaning it is via TV aerial and land based masts. So it is nothing to do with satellite.
My system also has difficulties on weaker channels when there is very heavy rain, which I believe ‘blocks’ the signal.
Yes, In rain / heavy cloud, the weaker signal cannot make it through, so reception is lost, even on the large 2,4m dishes. I have never lost TDT signals, even in the heaviest of rain, but have done in some really hot and humid summers, as the heat can play havoc with TDT signals.
I have never noticed any problem with Spanish TV which comes from the community aerial. I think the signal from that aerial is a TDT signal.
Correct. But if the system is not correctly aligned, of the amplifer / distribution unit is not correctly configured, or the cables from apartment to apartment are not good, or there are poor connections.