As hosts we tend to assume that guests are simply not bothering to respond to our Airbnb messages, which is often true, but not always. If a guest hasn't answered my message, I'll try again, stating its importance, and if there is still no response, like Helen, I'll asked Airbnb to try to contact the guest, which has resulted in a response. Some guests don't know to turn their notifications on, so you can always try sending them a text message on their phone, or calling, asking them to please check and respond to their Airbnb messages.
A couple times guests didn't respond in a timely manner it turned out they were on a camping trip with no internet or cell signal, or at a retreat where they weren't allowed to use any devices, and once the guest said she had never received any of my messages, which I did believe, because she apologized profusely. Glitches are quite common on this platform.
As far as IB pre-booking messages, I can't speak to that, as I've never used IB.
@Jacob470