Got a couple relevant comments from thethirdposition archive

Stennes

I can think of a few. They're not so famous today, but they were well-known figures in Germany during the '20s & '30s:

Josef “Beppo” Römer - leader of the Freikorps Bund Oberland; later moved to the left, taking a portion of his men with him & becoming Rechtsbolschewisten ('Bolsheviks of the right'). Was executed during the Third Reich.

Bodo Uhse - prominent NS journalist who took part in the Schleswig-Holstein Landvolk struggle. Grew disillusioned with the NSDAP, briefly left it for the Strasser-group, then joined the KPD. Became a famous writer in East Germany.

Arnolt Bronnen - prominent Expressionist playwright who shocked his friends (including Bertolt Brecht) by moving from the left to support for the NSDAP. Was friends with Goebbels and hung out with Niekisch, Jünger, Otto Strasser, Ernst von Salomon. Was kind of an asshole. Struggled during the Third Reich because of suspected Jewish ancestry and became an ardent communist towards the end of WWII.

Ernst Niekisch - started on the far-left (he was a significant figure in the Bavarian SPD & USPD), then moved towards national-revolutionary politics. He was treated abominably during the '30s (imprisoned & tortured by the Gestapo for suspected treason, suffered permanent vision damage). Became a communist again while locked up and was relatively high-up in the East German government, until he grew disillusioned after the crackdown on the Berlin Uprising and fled to West Germany.

Bruno von Salomon - brother of famous nationalist writer Ernst von Salomon. Started off as a nationalist, supporting the peasants in the Landvolk struggle. He & Bodo Uhse converted to communism together. He fled Germany during the Reich and iirc died of alcoholism after the War.

Richard Scheringer - Very famous case. Was a young junior officer in the Reichswehr. He and two friends (Hanns Ludin and Hans Wendt) were taken to court for spreading nationalist & NS propaganda amongst the soldiers. Hitler famously spoke at their trial; his words helped disillusion Scheringer. Scheringer was converted to communism while in jail (Ludin joined the SA after he was released; Wendt joined the Strasser-group). After Scheringer was released from jail he was used as propaganda by the communists to try and convert other nationalists. He stayed friends with Ludin; Ludin protected him during the Third Reich and they fought together in WWII. After the War Scheringer couldn't prevent the communist authorities in Czechoslovakia from demanding Ludin's death, although he tried. Scheringer became a prominent KPD/DKP (communist) politician in West Germany after the War. His children & grand-children are still prominent in the Left Party.

Those are the most famous German cases I can think of right now, although I'm sure there are others. Most of them have Wiki pages with more info. There were lots of less-famous nationalist converts in Germany as well, though. The KPD adopted a new program in August 1930 which was specifically written to appeal to nationalists, to voters who might be lured to the NSDAP. Scheringer's conversion helped them - he became the face of their new 'national-bolshevik' campaign. In the 1931-to-early-1933 period especially there was a lot of drifting from Brown to Red (or vice versa, and sometimes back again...). The Strasser-group was kind of a transition-point for people switching from one side to the other, they'd often pass through it first (which I'm sure frustrated Otto). The NSDAP's strong socialist rhetoric, and the KPD's heightened nationalist rhetoric, created a confused situation - there were plenty of people who'd have been happy with either party in charge so long as they got socialism and a strong Germany again.

Me

Interesting, seems like most of them remained nationalist and just switched based on economic differences, kind of like how a left and right emerge in Liberalism or anywhere else I suppose. Are there any that went full International Socialist completely renouncing nationalism and race politics?

Richard Scheringer - Very famous case. Was a young junior officer in the Reichswehr. He and two friends (Hanns Ludin and Hans Wendt) were taken to court for spreading nationalist & NS propaganda amongst the soldiers. Hitler famously spoke at their trial; his words helped disillusion Scheringer. Scheringer was converted to communism while in jail

Can you explain this? Wouldn't Hitler have been defending him if he was spreading nationalist propaganda? How would Hitler have made him disillusioned? Sounds weird. Thanks for the comment btw, good info here.

Stennes

Interesting, seems like most of them remained nationalist and just switched based on economic differences... Are there any that went full International Socialist completely renouncing nationalism and race politics?

This is my assessment too - they might have joined or supported the KPD, but they were basically National-Bolsheviks during the Weimar/Third Reich era. As far as I'm aware all of them who survived the Hitler-period did eventually renounce their earlier radical-nationalism after the War, though - Scheringer went from a gung-ho militarist to a strong advocate for peace and internationalism, for instance (although he never demanded the USSR disarm itself, of course, just the Western imperialists). Bronnen and Uhse became orthodox Marxist-Leninists who supported whatever the Soviet line was (although Uhse grew to have doubts). I'm not sure about Niekisch, since his ideas as a nationalist were so eccentric already, but I suspect like a lot of people the excesses of the NS era pushed him away from strong völkisch ideals. It's complicated by the emergence of East Germany, though - plenty of people (encouraged by the state) just swapped out their pan-German nationalism for a new patriotism towards the "socialist fatherland" of the DDR, bound up at the same time in the idea of "international socialist brotherhood" with other communist nations. Some examples of this nationalist/patriotic slogan in the DDR - unser sozialistisches Vaterland, 'our socialist fatherland'.

Can you explain this? Wouldn't Hitler have been defending him if he was spreading nationalist propaganda? How would Hitler have made him disillusioned? Sounds weird. Thanks for the comment btw, good info here.

I cut out some detail to not make the post too long. The 3 junior officers had been spreading propaganda specifically to encourage the soldiers not to fight against any revolution led by the NSDAP or other nationalist groups if it broke out - they were trying to encourage them to join any potential 'national revolution'. Hitler shocked them at the Ulm Reichswehr trial. He very famously used the trial as a platform to officially declare that his party was not seeking to overthrow the state, that he was trying to attain power legally - that after he was legally elected there would be a legal revolution and "heads would roll", but in the meantime the NSDAP was entirely law-abiding.

Hitler's actions at the trial reassured a lot of ordinary citizens who were still worried about the NSDAP being too radical; they gave it a little bit more of a respectable veneer. But he pissed off a lot of the more revolutionary nationalists, who viewed cooperation with the system via elections as unbecoming or a betrayal. Scheringer saw it that way, but also saw it as Hitler basically throwing them under the bus - even though they'd been supporting the Party with their actions, and had been celebrated by & courted by the Party. Hitler's actions combined with other things which had discouraged him. Goebbels visited them all in prison, for example, and Scheringer was put off by him. At some point before the trial, too, he'd been given a tour of the newly-built Brown House in Munich (the official Party HQ) and was shocked at how grand and opulent it was, how many thousands of Marks had been spent on it while he knew there were so many penniless SA men out there who couldn't afford uniforms or proper meals. Ludin & Wendt were also very put off by Hitler at the trial, but Ludin decided to stick with the NSDAP & SA. He became an ambassador to Slovakia, which is why he was executed at the end of the War - he was accused of war crimes.