Have you ever had a Surpass before this? The new T&C limit the bonus to once per lifetime. So if you had a Surpass before this upgrade, you won't get the bonus. There was a thread on this at the time I upgraded. Let me see if I can find it.

Edit: found it. As of April, 2017, the language in the T&C on upgrading to Surpass states:
Important limitation on this offer: "Welcome bonus offer not available to applicants who have or have had this product."
The thread is here Ongoing offers for Hilton cards issued by Amex or Citi and the discussion of the 'once per lifetime' exclusion starts at post #1167 .

Someone first noticed it here: https://www.flyertalk.com/forum/28173985-post1167.html. There was a link at the time that went to a copy of the former T&C without the mention of not having held a Surpass previously but that is long gone now.

So if you have ever held a Surpass in the past, that could be why you didn't get the bonus since you applied after they changed the rules in April. Even if you got a letter or offer to upgrade on your account, if you have had a Surpass previously, you don't get the bonus. The system doesn't verify whether you are actually eligible for the bonus when sending the offer to upgrade - it is just an offer to upgrade. You still have to meet all the requirements in the T&C. If this is your first ever Surpass, then just disregard all of this