ᐅ Insulation is visible on the exterior facade

Hello ladies and gentlemen,

For several months now, the pattern of the insulation boards has become increasingly visible on the facade of our house. The plaster is not dirty; rather, the insulation seems to be showing through. It looks really strange and is somewhat difficult to describe.

The house was built in 1980 and consists of 36.5 cm (14 inches) lightweight aggregate masonry, with a 5 cm (2 inch) thick expanded polystyrene insulation layer, reinforced mesh, and finally mineral render on the outside.

There are two special factors: I painted the facade with a Lotus-effect paint, and in winter the house remains unoccupied for several months and is only minimally heated.

Given these conditions: What could cause the outlines to appear on the insulation, and what can I do to address this? Thank you for any information!

What becomes visible are the joints of the insulation panels; these joints have a higher thermal transmittance than the insulation panels themselves, creating thermal bridges at these points. This leads to condensation, and dust, pollen, etc. accumulate here, resulting in a visible pattern of joints.
This is not related to the Lotusan coating.
There is little that can be done about it; this visible joint pattern is common in houses built in the 1980s. Back then, the joints were sealed with mortar, whereas today spray foam insulation is used.
A costly but effective solution would be to add a second layer of insulation. Otherwise, you have no way to permanently control the problem.

A new coat of paint wouldn't eliminate the cause, but if the result lasted several years, I would definitely consider it worthwhile. Is it possible to estimate how long it takes before the pattern of the joints becomes visible again on a freshly painted facade?

A single coat of paint is not the issue; it would only temporarily cover up the problem. Unfortunately, it is not possible to predict how long that would last.