Once a desert zone has been searched several times, it can become "depleted" which means that no more useful objects can be found there. At best, poor quality materials (wood and metal) will be found.
However, for several weeks now, we have observed strange meteorological phenomena occuring during the night in the World Beyond...
Violent sandstorms rage in the World Beyond around 23h00 (server time). No rational explanation for these phenomena has been found at this time.
The good news is that in affected regions, these storms can uncover new objects even in zones which were previously considered depleted.
To find these zones, you will need to build a Search Tower (construction site). Furthermore, upgrading the Search Tower improves the chances that affected zones will regenerate.