Inconsistent/glitches?

Ran a webinar today but I have never experienced the range of technical issues on Zoom that I have today.

Some people could hear me, others couldn't; some could see slides from share screen, others couldn't; for some it froze on one slide and wouldn't move along, but for others it was fine.

People went out and came back in - usually to no avail; I stopped sharing and then restarted which fixed it for a bit then I had to stop and restart again and it was fine for the rest of the webinar.

All in all, frankly a nightmare.

Any thoughts?

Thanks