I had a realisation that Samsung J-series TVs run apps which are web-browser based, and therefore could be breaking due to a NowTV app update conflicting with something lingering around in the browser's cache which shouldn't be there.
(I've seen this sort of thing happen in regular web apps sometimes - browsers try to be efficient in avoiding re-downloading the same files every time you load the same page/app, which is nice until it misses the fact that the files it's avoiding re-downloading have been updated since the last time they were fetched).
This is what eventually worked for me to reset/clear out the cache:
1) Open the Web Browser application
2) Click on the menu icon in the top-right corner
3) Go to Settings
4) Select Privacy & Security from the left-hand side menu
5) Scroll all the way to the bottom and click on the Delete Browsing Data option
6) Click on Yes to confirm clearing cache.
If this hadn't worked, my next step would have been to reset the Smart Hub altogether, although that option is annoying because it means setting everything up all over again from scratch.
Note: I've no idea what specifically might have been in the cache - I'd suspect an outdated script file causing the TV/browser not to bother updating/refreshing to NowTV's latest script files. Alternatively maybe the app updated but some persistent session data or cookie might have been lingering and the app just didn't know how to handle it.
I did not go as far as enabling the TV's developer mode to try digging out log files to see whether that would reveal the real problem, though the frustration was pushing me toward that point.
Feedback for the NowTV app dev team - please add a test to your release workflow for updates against older J-Series TVs (Tizen 2.3).
