This. I think 
If it helps, today I spoke to a friend who claimed the bug does not happen in private/pre-made games at all . So I completed all bounties alone, with the buff, invited a friend, and we both got double bounties.
Still sucks that I have to relog till I get the buff but now at least I may have a way to keep it active.
Hello all! This should have been fixed as per a notice from General Discussion about the EU buff.
@MissCheetah : Thank you for stepping in and helping to solve this issue.
It is not completely resolved. An hour and a half or two ago, on the EU server, I only got one box from Act 4. Got two from the rest. Left game and next time I got two from all places. Didn’t notice any buff for this showing up either time, but I probably just missed it. Oh well, not that much trouble.
Edit: PC here.
Not getting double bounties on the Switch. Also not getting any kind of notification that double bounties are active. I’m in California.
Now the LB validation please, why take that so long?
The EU LB issue? I know it is under investigation but I don’t know if they have nailed down a cause, or more importantly, a solution. They will update us when the QA and Devs have something to share with the Community Managers/Lead.