This is an interesting situation and has never happened to me although I have attended hundreds and hundreds of hours of mathematics lectures.
It did happen once that a lecturer swore under his breath once or twice because the software for giving virtual talks was so useless, but it was more of a humorous moment and everyone understood his frustration. In that case, it was more out of frustration, and not for actual deliberate emphasis, which seems unprofessional and which I have not encountered even after attending several hundreds of hours of lectures.