Why is lag worse in online multiplayer than in single-player?

Because there’s an extra step in the loop. In an offline game, your input travels to our servers and the video comes back. In an online game the round trip also passes through the game’s own servers, which makes it longer.

This is normal for all cloud gaming, not something specific to Aristeem Play.

If the picture breaks up or blurs rather than feeling delayed, that’s a bandwidth problem instead — lower the stream quality and it will stabilise.