Two words, no hints
The post asks "Do you know another two words?" and this time spells out the format: the two words in normal capitalization with a space between them, then a space, then the last three characters of the block 5 key, KPb. SHA-256, entropy, m/44'/0'/0'/0/0, same as before. The author called it fairly difficult and gave no hints.
Nobody got it that day. The first update says "No one came up with the two words I was looking for" and gives up only the last three characters of the key, MQz, because block 7 needed them to go on. The prize stayed up for whoever cracked it first, "obvious in hindsight".
The words were "Thank you". The author's last edit admits the joke: every block from 7 on opens with those two words, so the answer sat in plain sight in the next question. The string that derives the key is Thank you KPb. The spaces count, and so do the capital T and the lowercase y.
Claimed before the answer
Funded at 16:18:11 UTC on April 7, three hours after the post, and claimed at 11:26:31 the next day for 666,438 satoshis. Fourteen minutes after the claim a commenter wrote "Thank you" from someone called PonkyPink, and the author answered "You are welcome :)". The edit with the words came after that. The record says solved, because the answer is public, and names nobody, because the chain doesn't say who PonkyPink is.