Update: A USK representative replied to clarify that German authorities are not considering a general ban on loot boxes, but are actually examining regulations of online advertising and purchasing as a whole.
"A closer look at the discussion is taking place, ie., if there are any specific risks and where to locate them legally. As part of that analysis the KJM (governmental institution responsible for youth protection regarding to online content/services) is taking a closer look at permitted and prohibited advertising in shop offerings. However these rules apply to online purchases in general, thus also to loot boxes," the rep said.
"In the German debate this term [loot box] refers to a broad variety of different in-game or even just game-related purchase systems with more or less randomized items. Hence one cannot say that 'loot boxes' violate German laws, as each integration has to be evaluated as separate case."
Germany is looking into imposing restrictions on loot boxes in videogames, according to this Welt report, which says (via Google Translate, so caveats apply) that a study by the University of Hamburg has found that elements of gambling are becoming increasingly common in videogames. It's an important part of the game industry's business model, but the chairman of the Youth Protection Commission of the State Media Authorities warned that it may violate laws against promoting gambling to children and adolescents.
Germany's Media Authorities join a chorus of loot box critics from countries including Belgium, Australia, and the United States, all of whom have suggested that RNG loot drops that require real-money purchases could be, or should be, subject to some form of regulation above and beyond ESRB age ratings.
That position runs counter to opinions expressed by videogame publishers and rating agencies, including the ESRB in North America and PEGI and Ukie in Europe. Germany's USK rating board hasn't weighed in yet, but PEGI operations director Dirk Bosmans said in October last year that he believes it holds the same position: That "we cannot define what constitutes gambling," and therefore cannot regulate loot boxes as such.
The Youth Protection Commission will render its decision on loot boxes in March, according to the report. I've reached out to the USK for more information and will update if I receive a reply.