If they are a busy model, who is doing something else at the time, and your tip is small, yes, this could happen.
Traffic seems to be feast or famine, all at once, or not at all. So when it does come, we have to filter out who the highest priority for our attention is, based on past history and current spending.
If you send a model a 5 or even 20 token tip, when she's in the middle of a conversation with a guy who has spent $1000s on them, over the course of time. Yes, you likely won't get a huge response.
Just like if other guys are tipping for action, but you're one of those dudes who wants to ask a lot of questions first, the model is going to follow the money. The guys who are already ready, and decided on what they want. Guy's will be dropping tips, and I'll be in the middle of performing, then some dude comes in and will be like; "Hi I'm Dave from Ontario, I'm 47, how are you doing today?". I'm not going to stop and acknowledge that or respond. Because it's a bit self absorbed on Dave's part, and a total mood killer for the rest of us. The number of people who just arrive, and pay no attention to what is currently happening in the room, is surprisingly high. If nothing was going on in my room, I'd likely respond, but it really depends what is going on already, and my mood.