I've heard the expression can be able to consistently from a couple of folks from India, Malaysia, the Philippines and Vietnam. Here are a couple of paraphrased examples:
By signing up to our service, you can be able to access to our discount programs.
You need to learn the system so you can be able to navigate the guests to the correct menus.
Granted, these folks' English is kind of funny and often full of true grammatical errors, but when it comes to can be able, it doesn't feel like just a offhand mistake made by non-native speakers. The folks I've met or heard from seem to consistently use it as a stock expression: they noticeably never use just can, nor just be able to; they always say can be able to, though some of them do just use cannot without be able to. It's so noticeable that oftentimes I can't hear anything they say other than all the innumerable instances of can be able. I've never heard it from native speakers, or seen it in any texts written by native speakers. I don't recall ever learning in English classes, or seeing it in any English textbook. It's apparently redundant, too, and I can't figure out for the life of me what could possible make it a thing. Even if it was supposed to be for emphasis, why would you emphasize all the time?
The more I try to look into it, the less convincing it seems that it's an idiomatic expression among native speakers. It is vanishingly rare in whatever corpus Google Books has, with only 2 matches on the first page of the search results. The consensus among Quora answerers seems to be that it's probably grammatically correct, but not idiomatic, as in "you can technically say it, but why would you?" One Quora user named Ben Roffey proposed a context in which it can plausibly occur, but even then he still acknowledged how awkward it sounded, still. Some Reuters articles feature multiple occurrences of it, although they're all quoted from, additionally, speakers from Africa and Europe.
So, disregarding grammatical correctness, is can be able to idiomatic among native speakers? If not, what could possibly be the logic behind it, and how did it arise?