YouTube Offline Videos deleted/removed I download few YouTube videos using YouTube Offline feature introduced recently in an Official YouTube App.

Those videos were accessible to me and I played them successfully, without any issue.

Because of some device issue, I happened to "uninstall updates" of YouTube App. 
and now I had an old version of YouTube.

I then took the update of YouTube app as I wanted to enjoy the new Offline feature from Google Play store, which had the Offline feature.

But when I went to "Offline" tab in my YouTube App's Navigation Drawer (After Update), I could not see my previously downloaded videos.

Of course, I used same Google Account for my YouTube Sign-in.

So, let me just re-phrase the issue:

Whenever YouTube App's Updates are uninstalled, all offline Videos too are removed.

And when I update YouTube app later(which has Offline feature), App does not contain previously downloaded videos!

Any ideas, how can I get my lost videos??
The "offline feature" rather counts as cache (note that content downloaded for offline use will be available this way for 2 days only), so it's not considered "your data". You performed a factory-reset. From our factory-reset tag-wiki:


  What a factory reset does is basically to "wipe" (delete all content) from the /cache (holding the application cache) and /data (user data and user-installed apps, dalvik cache) partitions. Other media, like internal-sd and external-sd cards, are usually left untouched – though some devices/ROMs offer options to include them with the wipe.


So that includes your "files cached for offline use".

Also, as correctly pointed out by GiantTree, your comparison with several apps does not apply: Google Drive stores your data in the cloud (not on the device), same for most other "Google Apps". Nor do photos made with a camera app get wiped usually, because they are not affected by a factory reset (see above quote for SD cards).