I have found reference to an auto-loading shotgun on pages 215-217 of "Walther, A German Legend", by Manfred Kersten. This shotgun was invented by Carl Walther in 1921, produced by Walther for a while, then turned over to the Deutsche Werke company for further sales. Internally, the shotgun works like an upside-down Luger, with a toggle that "breaks" downwards (the pages covering this shotgun are titled "Die Kniegelink-Flinte" / "the knee-link shotgun"). The magazine is contained wholly in the forearm, the rear of which swings down from the receiver to load, and the factory specs on this shotgun say it should have a 27.5" barrel.
The Blue Book (25th ed) shows the Walther semi-auto shotgun as made in Zella Mehlis [Thur] from 1921 to 1931, with a top value of $875, which seems reasonable and would probably be about $1000 today. They are more desireable to Walther collectors than they would be as hunting shotguns.
A blurb detailing a reprint of the 1934 Walther catalogue notes that - 'Walther’s only two hunting guns are shown in this reprint. They are side by side shotguns that are typical of the 1934 period in Germany. Both have Purdey-style dual under-lugs, utilize the Anson-Deeley boxlock design, and have the Greener cross-bolt locking system. These are the Models WSF and WSFD. For years an argument has been going on about whether Walther actually made these doublebarrel shotguns or not. Their ‘forte,’ or primary market, definitely was not in hunting guns of any type. Perhaps someday someone will definitely prove Walther did, in fact, make these double barrel guns. There was nothing different, fancy or unique about these guns.
There are also vague hints of a side-by-side combination shotgun and rifle, known in British circles as a Cape Gun, but I can't find any more about it.