I have a couple questions about the artifacts.

Does it keep track in real time of the 3 you have in play for both games, or does it depend what 3 you have in play at the time you leave or come back to the level? It's important because I have one of those 20 minute plus idle time artifacts, so it makes a significant difference.

To be honest the one time I used play two lvls at once I didn't do any swapping, so sorry didn't get to test that at all... did find out you can only dig in one or the other so it really delayed that 2nd game... my assumption would be if you change an active art its the same in both levels

Yeah, you can't start a dig on a new level if you are still in one from the previous, so I figured they wouldn't give you a second one if you did multi-level.

I'm not sure if you change the artifact it works in real time in both levels because that would be much more complex to program and would be much more of a burden on their servers. It seems more likely it would either remember what you had when you left or would read what you have in play when you return. The first could be ruined if you change devices or clear your cache/cookies. I don't know how often it updates and transmits your progress to the server.

I know that the game works perfectly fine when you are offline. I've found there are some issues if you close out of the browser before reconnecting. My wifi goes out every time someone uses the microwave.

You have only one artifact setup for any number of maps you're playing simultaneously. The latest three you have equipped work for all maps at the same time.