Slow channel change, slow app loading, and freezing in apps such as Apple+

Channel changes are slow, apps load very slowly, and playback often freezes on certain apps such as Apple+.  My wife often falls asleep waiting for things to load.

I am frustrated that the Xfinity Assistant doesn't include the option to try dealing with this.  I have new batteries in the remote and have re-paired it, have restarted the modem and the Comcast box several times, with the same behavior.  Using my Roku stick, the applications load immediately and work flawlessly, including the Xfinity streaming app, but the Xfinity app has fewer functions and in any case I expect the set top box to work properly.  I moved from TiVo to the Xfinity box but its performance pales in comparison to TiVo's, which not only had immediate response but included non-jerky fast forward, and slow motion.