@Retired Engineer and others...
About a week before the FW upgrade, I had the same issue where 90% of my recordings appeared to disappear on my desktop using Chrome.
I then launched Firefox on the same desktop and all my recordings appeared.
Went back to Chrome and in Settings, cleared all my cookies, cache and stored data. Like magic, all my recording then re-appeared on the Chrome browser. I did not power cycle any of my equipment (Tablo, router, PC).
My conclusion was that Chrome stored something that kept it (Chrome) from accessing or displaying the Tablo recordings correctly.
So, for those that are using web browsers to watch their Tablo's and having problems, my advice is to make sure and clear your browser's saved data (cookies, cache and stored data). It's worth a try.
Hope this will help others who are having problems with 'lost' recordings.
For what it's worth... I did upgrade my Tablo FW yesterday. Took all of 2-3 minutes and it went very smoothly, without any issues.