So this has happened on at least 3 separate occasions -- I have learned some recipes only to find them sitting in my inventory unlearned some time later. This latest time it happened -- it was a purple and blue blueprint that I had JUST learned. I relogged the character because the game is broken, and when I came back in, they were sitting in my inventory again, unlearned.
What I worry about is, if this can happen, what else may be happening that I am unaware of, like blueprints going missing or otherwise not being tagged as learned (which I feel certain has happened, but dont have any objective evidence).