I dont actually think there is much difference.
User 1 logs in (subscribe to Topic 1)
User 2 logs in (subscribe to Topic 2)
Event is pushed to topic 1: ok
Event is pushed to topic 2: ok
User 1 refreshes browser
Event is pushed to Topic 1: Both users get the same data
As soon as I refresh one of those browser windows it seems to start pushing messages to both users.
If i get time I will try setup a test project to see if i can get this to happen again. might help clear some of my code too.
I finally managed to reproduce it - it looks like the it happens not only while refresh, and the order of opened browsers matters. Thanks a lot for finding it out!
Ecto is completely independent from Drab. I did not test Phx 1.4 yet, I will do it during incoming week.
I’ve been running Drab on Phx1.4 for a day now without any big issues noticed as of yet. 
I noticed in v0.10.0 Drab is set to require plug_cowboy 1.x – Drab (seemingly) worked for me with plug_cowboy 2.x. Did you find a reason to lock it down to 1.x?