If you're talking about Steam and not the Client itself, I think I have the same issue..
Actually, both. Steam DID download extra 3 Gb, but that's about it. Then it launched the ESO Launcher, where it said that it needs to download 47 Gb, but that number stayed the same throughout percentage, so I guess it just did a checkup.
FFS, there it goes AGAIN! Third time this week, I am growing tired of this.
I identified when that happens, the game is on a Seagate 1TB HDD, connected through USB, and when all this happens I hear a distinct "plugged out" Windows sound when I start the Launcher through Steam. Steam started downloading 3Gb again.
Edit: now the Launcher couldn't update manifesto or something, and it says "Creating Download" for the same 47Gb as before (but before it was verifying).
Edit 2: ok, one eternity later, it actually just verified and downloaded 2Gb (after Steam did 3Gb). How do I avoid the whole Steam DL/Launcher Verification procedure after the stuff triggering this happens? It is starting to drive me nuts.