Rock bands use massive monitor speakers to hear themselves play in a concert. When you run a virtual presentation, you need something similar. Slide transitions can be delayed especially when you use high res images. You are on the next page, but your audience is not.
To prevent this, log into your own webinar with a second computer, or even an iPad or internet-enabled smart phone to see what your audience is seeing. The really skillful presenter switches slides on his own computer but continues to talk about the slide that is still in front of the audience.
Image by Anirudh Koul