Only new tasks appearing in To Do web

MBookfielder In my case the problem resolved itself in a day or two. Obviously like you I was very reluctant to sign out of the mobile endpoint that was still showing all the tasks given the risk of losing them all if they're not synced. However the first sign that things were working again showed up for me when I signed into an additional To Do web endpoint (in incognito mode, in a separate browser, so there was guaranteed to be no leftover caching or cookies) and my tasks started showing there. Once that worked I signed out of the original web endpoint and signed back in, and that one worked again as well. Perhaps give that a try.