This happened a couple of times with me last year, both involving requests for full manuscripts. One requested the full about 3 months after the query (I was actually planning on marking it CNR that very day), and the the other requested it nearly 9 months after the query!
Of the two, the first one seems to have ghosted on me (it's been nearly a year), which is the only type of ghosting that actually annoys me; I'm in the camp of heavily sympathizing with agents in terms of how many queries they receive, so I don't find the no-reply tactic on that front particularly bothersome. But when you've requested a full manuscript, and the author nudges a couple of times... at least have the courtesy to say "thanks, but no thanks"!
The second one send her request after I was already deep into my latest revisions. I asked if I could send her the new version when it's ready, and she said yes. So once this draft is done, I already have a full request straight out of the gate, which seems nice.