So, a couple of days ago this thread caught my eye, since I also was unable to see DaVinci ANYMORE (i.e. I had played vs him before, so please spare me "the problem is always the user"-feedback-questions if I actually earned him, which seems to be the standard procedure from what I've seen here)

Gladly, the user figured out the issue himself - he wasn't logged in anymore.

So I checked - and that was my problem as well.

However, even though it's fixed for now, I find this highly problematic.

The DaVinci persona is only available to play when 

a) You are actually connected to the internet 

AND

b) Ingame connected to your G2G account.

In general, I think this is a bad decision. 

What makes it even worse is that the game disconnects my g2g account AT LEAST when I lose connection to the internet AND doesn't even save my login credentials!

So everytime I want to play a new game (also via the random enemy generator) that includes the persona I earned I first need to manually check if I'm currently connected to G2G ingame (I actually need to take extra steps because it's not visible anywhere), then I need to look up my login and then log in manually ingame.

All that 100% unneccessary hassle makes me not want to play the game.

From my point of view this is the worst possible, most user unfriendly approach to this.

I urge you to do this another way.

From a technical point of view, it should be no problem - the check if someone completed the requirements only had to occur exactly once, since the event is over, not every time someone plays the game - therefore when that check occurs and is confirmed the game should permanently download the persona.