Why were some of my apps randomly deleted?

I just decided to update my iPad 2 to the latest version, iOS 9.2.1 yesterday to download this game (Fantasy War Tactics, heard of it?), and wasn't aware of what I'm about to tell you now. I admit I have a lot of apps, but not too many that the storage space is overwhelmed. Just today, as of right now, I checked one of my apps to see that it was not there. Actually, make that quite a few. QUITE A FEW apps were missing, and I don't know if I can ever get my data back by downloading it again… And here I thought the new versions were supposed to be improvements, not FAILURES. I know I did not delete them myself. I've tried rebooting it… But I'm too afraid to make a move by going on to the settings part because if I try to get them back (if I can) with the iCloud backup, things might get even messier. Needless to say, I'm not risking my whole iPad to get those few apps back.
Added (1). I've noticed some new apps like Tips, Find iPhone, and Find Friends downloaded on there. I don't know for positive, but I'm pretty sure that if they had new content in the new version, they still wouldn't have to delete some of my apps for it. That's my theory. I had the required amount of GBS left, so surely they didn't have to delete some of my apps to make room for theirs?! Besides, those new apps seem useless for me.

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