It's not really a "little thing" honestly, but lately I've been playing raids with a friend while he streams, and holy shit I had never realized how actually bad the raids online was.
The desyncronization is absolutely atrocious, I see actions happening in different order on my screen and his, even sometimes things happening on his screen first (note: being a stream, I'm seeing it with 15 seconds delay, meaning that actions are happening on his side almost 20 secs before me).
Remember when the raid for example stops for a few seconds (sometimes 10-15 seconds) with nothing happening? That's often due to animations still going on another person's screen because on yours something like a shield break or field condition already played, but on his hadn't!
Also field effects happening at different times, moves hitting in different order (have you ever wondered why sometimes you'd throw a big nuke through a shield that had no business hitting that hard? Usually it's cause actually someone else broke the shield and the hit landed after shield broke, but on your screen they shown in reverse. This also can happen in opposite way).
It's really really awful... much worse than it seems while playing normally.
I really love the concept of these raids and it's much better done than the SwSh ones but jeez GameFreaks, if you really CANNOT manage to have proper online syncronization, just stop. Don't even try.