Your upload speed is probably the issue. There a bunch of speed tests you can run (google has a good one) to measure your internet speeds. More than likely, if your upload is low (like under 2-3mbps) then you might experience problems streaming at high bitrates and high quality.

You also mentioned you’re on WiFi. Wifi is naturally unstable and fluctuates massively. Coupled with having so many people/devices using it, it’s probably fluctuating even more so. A wired connection is the most stable internet you’ll get.

Finally, frames can drop if Twitch’s ingest servers are having a bad day, but that’s nothing you can fix. And that won’t be a long lasting impact. If you’re seeing this issue like daily, then it’s most likely related to the first two things I said.