In addition to point 2. In my experience I also noticed a laggy interface starting with versions after 1.20.2. There is also a forum thread discussing this => Home screen scrolling is not smooth on 1.21.1, but is better on 1.17.0
Slow loading of items, however (different issue) could be (partly) solved as nibbles described it.
=> Plex HTPC slow item loading - #28 by nibbles
