missing slides

[Rojonia]

I have several times experienced the following - most recently today in the middle of a live webinar. After a certain number of slides (in the example today 16 out of 20), I can no longer bring up any of the following slides although they are available and should clearly be part of the presentation.

How is this possible? Is there any technical way that this can be programmed? (i.e. some kind of limit on the number of slides)? I may have done something without being aware. It is most annoying and has happened several times. I always take a hard copy with me just in case it happens again, but it is very unprofessional when I have to "wing it".