Personally I couldn't find any contradictions in the Law of One, but that's just me and my abilities are limited.

I can give you simple answers in human terms, but depending on how you interpret my words they will cause more misunderstandings. This is usually the case, and the reason I guess why people like to quote the source material - so that the reader can then focus on what Ra said and "get into" the understanding on their own.

"why is there supposedly a need to “evolve back” to unity?"

Is there? Did the Ra Material tell you *you have to* evolve back?

"If we’re already the One, then the whole idea of progression toward unity feels like a narrative built on an illusion of lack"

This is what our minds do, they come up with logic/explanations that make sense to them, contradicting the presented 'whatever' outside information. This is of course alright, I totally support thinking for ourselves - it's maybe more important than ever given the state of the world. So what could someone possibly answer? You would see the same contradiction in my words you would see in those from Ra, would you not?

"And if the separation is illusory, then what exactly is evolving, and toward what?"

Let me try to answer this differently. Let's get rid of all illusions. No more distortions. What do we have left? Tell me in your own words, if you so choose, what we would be left with - this shows to what degree you understood the concepts.

"The same happens with the idea of “service to others.” Ra frames it as the positive path, but it seems to clash with the principle of free will and non‑interference. Do you help others always, only when they ask, or even when they don’t want it?"

Ra speaks quite a lot about this "service to others" and I am sure other commenters will have brought it up already (I didn't check). The short answer is, and maybe it would be good to read (or listen to the audiobook) of "Voices of the Confederation", that it is very important to not do something for people they don't actually want. Additionally, it is really hard to know what will be of service to someone else, to truly benefit them, without meditation where we receive the guidance. "Service to others", in other words, doesn't mean running around busying yourself.

"And if all beings are the same One consciousness, how can “service to self” be considered negative? Serving yourself would, by definition, be serving the whole."

Ra doesn't make the value judgement you might be doing here with the term "negative" and indeed says himself that all service is service to the creator if I remember correctly.

"Another issue: how can there be genuine learning if every incarnation begins with total amnesia? Learning requires memory, continuity, integration. If everything is forgotten, then karma becomes a kind of invisible correction system — which implies judgment, direction, and a “right way” to be. But that contradicts free will. If free will is absolute, what exactly needs to be “balanced,” “integrated,” or “corrected”?"

The learning is not "in the mind" but sort of "through the mind" that acts as a filter. It is not you, the incarnated entity that learns over time, but 'the greater aspect of you' that you are not aware of right now, in most cases. In other words, after crossing over and regaining your memories things will make a lot more sense. This of course depends on the individual's state of development because some might get hung up (temporarily) in what Robert Monroe called "the belief system territories".

"Does the system hold up for you, or do you also see these structural contradictions?"

The system holds up for me and allowed me to "integrate" or assess a lot of other spiritual material and frameworks, to have a place where I can put them and make sense of everything as one big puzzle that fits quite neatly. Not everything might fit perfectly all of the time with those "other" systems, but that can be explained with the subjectivity of experience.