I didn’t see this issue listed, so I’m noting it here, along with how I overcame it.
Devices involved were a recent two-tuner Tablo 2.2.10 and a current level of Mac Book Chrome browser.
The web-based app failed to list most recordings after working well for a few weeks… Additionally, most, not all, live channel program information became missing. Other devices continued to work normally. E.g. iPhone, iPad, Amazon FireStick, and Roku 3. I tried Opera (another vendor browser similar to Chrome), syncing it to the the Tablo. It worked!
Fix or Bypass: I disconnected the Chrome browser from my Tablo, and then re-connected it. That fixed the issue. The Tablo itself was always okay. It was the web-base app instance that seemed to lose some of its state.