I had a similar problem as well. Having sent seven mountaineer divisions in the Spanish Civil War, they disappeared into the void when the Communists split off. My lend-lease shifted to the new Spanish Commune, as well as a claim that I had sent volunteers, but I couldn't access the volunteer interface at all (as I wasn't allowed to send volunteers to rebels from the Republican government) and my volunteers disappeared from Spain entirely. This, paired with a direct Portuguese intervention, caused a chain reaction, and both Republicans and Communists capitulated to the Nationalists (who had been reduced to a couple of towns left prior to the splinter) within a few months. I never got my mountaineers back either.