have done the combines for Magnetic Leggings (reclaim) and Magnetic Pauldron (reclaim) a few times and they dont register as 'learned'
I am assuming you're checking your /outputfile recipes blacksmithing to confirm and not just on the success message in the UI? I just tested on povar and they learned just fine.
The UI is partly heavily borked. Rezoning, relogging or reloading the UI could correct that temporarily. This reminds me on the bugs in the achievement tags which are still there after years. Sometimes this could get corrected when sync'ing the time of the PC. Perhaps that helps Lilaxe temporarily until devs fix that behavior. Everbug feels sometimes like having the usability of a videorecorder of the 80ties or a hack from a linux-nerd. Playing Elden Ring shows that sadly more than ever...