The drop in signal of 2D is noticed all over Spain and other parts of Europe. I saw a report from someone in Norway complaining of the same thing. The theories floated above don't correspond with reality however. It's not local interference. It's not the sun hitting the satellite's antenna (if this was the case it would improve late evening after sunset. The opposite is the case) The ionosphere reflects short wave, but not microwave, I believe.
Dust & moisture do affect satellite signals but this doesn't explain the effect of 2D signals weakening every evening, every day of the year, at the same time.
The post above about stronger signal currently late at night is a result of 2D's batteries being switched on during eclipse. The satellite is moving through the earth's shadow at night for the next 2-3 weeks. This happens agaain in the autumn. Batteries are swiched on for eclipse protection and received signal on the ground goes up to daytime levels for about 40 minutes during eclipse. Many have observed this effect on the fringes. During the day at this time of year, signal is lost briefly in the morning due to sun outage.
The various theories in this and other forums on footprints moving are shot through of holes, as if the footprint really was moving daily then Norway would have better signal in the evening at Spain's expense. This doesn't happen. One engineer I spoke to ventured the explanation that the two polarities of the beam vary in relative intensity during the day, in a complex and unpredictable way, more noticeable the further out of footprint they are being received. At night in Spain, at least in Madrid where I used to live, horizontals are very weak at night, verticals much stronger. During the mornings it is the opposite.
I suspect there may be other factors, but the daily variation is most surely not dust, interference, moisture, sunlight, lower uplink power (how could this affect downlink?), or the ionosphere.
It is related the orbit not being perfect, the earth not being a perfect sphere, and variations in the amount of sunlight falling on the spacecraft's solar panels.