Have you tried loading the same things on the web ui? That would be my first suggestion, to help you see if it’s Sync or Lemm.ee. That’s what I would do, anyhow.
Maybe someone else has an actual answer for you, but until then, maybe you can test .
Oh duh. I tried the web UI which was fast when I first hit it logged out. After logging in it was very slow for the first two pages. But after that it was very fast on subsequent pages. Going back to sync every page call is still slower than the web UI.