Punctuation, for example.

And no, at least for the languages with which I'm familiar SOTA tokenizers tend to only capture the easy cases.

For example, the GPT-4 tokenizer breaks the first sentence of your post like so:

  What/ do/ you/ mean/ by/ non/-m/orp/heme/ lexical/ units/?

Notice how "morpheme" gets broken into three tokens, and none of them matches "morpheme"'s two morphemes. "Lexical" and "units" are each a single token, when they have three and two morphemes respectively.

Or in French, the word "cafetière" gets chopped willy-nilly into "c/afet/ière". The canonical breakdown is "cafe/t/ière".