I have a 60 inch Samsung TV with Roku built into it. When I connected my Galaxy S8, it used to lag and have choppy screen playback when mirroring. I tinkered with some settings on the Roku options on the TV and it eventually played flawlessly... Still does.
Now, I have a Roku ultra, Roku express, and premier. I have these hooked up to a smart Vizio TV (32inch) AND 32 inch regular flat screen LED TV (Sony) mirror my Hulu Netflix etc to it, and all of them lag. I hooked them up to the 60 inch screen, and they all lag. It plays whatever I'm mirroring for 10-15 seconds and the screen freezes on that frame for about 2 seconds. Sometimes it just pixelates and continues but jumps back into frame freezing for 2 seconds, every 10-15 seconds. Most of the time the audio continues and the screen catches up and plays normally. It's RARE, but there will be occasions it plays flawlessly. Now I have a new lg v40 phone and exact same results. Lg v40 mirrors flawlessly on the 60 inch TV just like the Galaxy s8 and I even plugged the sticks, and mobile rokus to the 60 inch and the 32 inch tvs and it still freezes. I've deleted all the apps off the rokus, restarted them, changed all the sound picture setting etc to basics, even factory resets AND updates. Nada, still freezes. How can I get these to play smoothly?
Hi- I was having a similar issue with mirroring. Weirdly, no problem when casting from my laptop to my Roku TV, but the kind of lag you describe when I'd cast from my Samsung Galaxy S10- even when I switched to a gigabit fiber optic connection! I didn't have this issue when I had a Roku Premiere attached to my prior TV. I knew I had to find a fix. Someone on Reddit suggested Allcast app for Android, and low and behold, it actually worked like a charm- I'm back to casting again! I tried a few other apps too- only this one worked right- why, I really don't know, just happy it's working. The free version will dismay ads on the smartphone screen, but not the TV, so I don't find it intrusive, but I'll likely go pro soon after a few more tests.
Given that my S10 was able to cast successfully before, either Roku, Android smart view or both have really dropped the ball. Hopefully they'll get this worked out soon, but in the meanwhile, I hope this workaround helps you and others.