Bandwidth, audio levels, mismatched cameras, no backup recording. The problems that bite most often, and how I handle each one.
https://www.youtube.com/embed/PM70uJfTdcs
The same handful of problems account for most live stream disasters. Here's each one and how I handle it.
A 1080p stream needs roughly 5 to 6 Mbps upload. I've walked into venues with 10 Mbps available, and that number drops as everyone else gets on the shared network. Test the upload speed before the event, using Google's speed test or Ookla. When it isn't there, I use a Teradek Prism Mobile, which bonds up to nine connections: 4G LTE modems, Wi-Fi and Ethernet. It has saved streams for me.
Blackmagic ATEM switchers are notorious for streaming a little quieter than you'd expect. Mic your presenters up before you go live and have them speak at real event volume, not a soundcheck mumble. Don't fear yellow on the meters. Occasional dips into red are fine. Just don't live in red, and don't live in green either. A bad picture with good audio keeps viewers. A 4K picture with bad audio loses them.
Sync your cameras beforehand so white balance, frame rate and output resolution all match. One camera at 1080p and another at 4K with mismatched frame rates reads as unprofessional the second you cut between them.
And run a pre-event checklist every single time, until it stops being a checklist and starts being a habit.