I have the same sync-problem once again, but only with new web-UI in my chrome browser: sync is frozen with last note from 9th september (there are quite al lot younger notes...)
If I open evernote web with new web-UI in my vivaldi browser I get all notes, even the the freshest, only a few minutes ago.
I guess, this could be a cache-problem? Probably lots of header and meta-infos like title, date edit, tags and so on might be locally saved in cache for fast response. (have you seen the update progress in waves, when you open for web browser after a cpule of days? note-header infos seem to be synced and updated in groups or waves..)
If this would be a bug in a kind of check-load-update-check-load-update-progress, the web-UI-sync may freeze like we see.
additional infos:
frozen again with note up to the September 7th
solved again in Chrome with logout and login on September 17th