Nothing ever lags excepts when I stream video playback from my phone to my TV using Screen Mirroring. Everything is updated and only screen mirroring lags. I can watch same video on each device without screen mirroring and the video doesn't lag so there must be problem with the screen mirroring service.
Do you mean non-responsive for a bit (shouldn’t be), or a constant but not interrupting short delay (as expected)?
Does it happen for every app with video services, or for a specific (set of) app(s)?
What is your model TV? Is its certified as AirPlay-enabled?
Select non-Apple apps on iPhone may support Chromecast (Google Cast) through the same interface, but which is outside of Apple’s support. So the distinction between AirPlay and Chromecast is important for this.
Use AirPlay to stream video or mirror the screen of your iPhone or iPad - Apple Support
If screen mirroring or streaming isn't working on your AirPlay-compatible device - Apple Support
If available, use in-app AirPlay controls instead of system-wide screen mirroring, for best results.
Unless someone else chimes in with a new idea, I would suggest to contact an expert from the Apple Support staff for further assistance. Contact Apple for support and service (phone numbers) or start your support request online (chat/email/callback).
The video playback lags for differing amounts of times and sometimes improves for short period of time if you hit pause and wait. It’s like there is buffering interference for transferring playback or there’s limit to WiFi transfer. I have newest Apple TV and Pro phone.
Warning Screen Mirroring Stream Always Lags and is only thing that ever lags
