if you use upb, go to setting than scroll unifi tv apps. click unifi tv apps than click clear data. after that, restart ur upb. after that, you need sign in unifi tv with ur id and ur password. don't forget, update ur unifi tv apps at google play store upb. The latest apps don't any lag.
please update ur android box to the latest version Android 10. go to setting, scroll and find about device. clik there and update ur upb to android 10.
After install android 10, go to setting than clear data unifi tv apps. After that, sing in again with ur unifi tv id and password.
I am upb too, my unifi tv very smooth after i update upb to Android 10.
Already go to Setting - Device Preferences - About. Here, Version 9 - then went to System Update - Check for update. Message is " Your system is up to date" - Version is still 9
The last thing I can imagine is the cable fault. I have been using this for 2 years and because the change of channels all these happen. I have to engage the contractor and pay RM200 to reinstall the cable.