No it didn't pop up just a while ago, the problem have been around since at least 2.0. I discovered it on 2.0 due to the new talent which requires me to use some mysteries mid-turn. Before that, most of my cast are up-front, so I can't be sure. So with the newly discovered lag, I tried a number of things to figure out where it actually came from, and it was discovered that chase is the root cause. Similar thing might have happened to you, your previous team or opponent might have had no need to have mid-turn cast such that even thou it's there, you didn't notice it.

Don't assume a problem didn't exist because you didn't personally notice it.

Thou to be fair, I have minimal amount of experience using ONLY animated mystery. Because most of my mystery and that of my opponent leads to chase afterwards. And if you intersect with the need to cast mystery in middle of turn, the amount of experience is small on that end. The server may or may not wait an appropriate amount of time for animated mystery w/o chase trigger.
I don't know if the problem exists in CN/DE/RU, but that's hardly relevant.

On the other hand, If you have random lags w/o chase, then that's probably you(again, not sure if animated mystery might be a cause, but if you have neither that nor chase...), either due to internet or flash.

And then there is the interesting bit about CPU spike.

Guess what, you SHOULD have CPU spike in combat. Because the battle is hardly "even" in terms of resource consumption. Normal attack that leads nowhere are the cheapest while flashy mystery should cause spikes compared to that. So if you are not spiking, that might mean you are maxing out your CPU utilization which means that during the time when you should have spike, you are lagging due to insufficient CPU horsepower.

And no, not having 100% CPU utilization does not mean you are not maxed out. CPU utilization that you see means the amount utilized across all cores. But this game only uses one. This means you could have one core spinning at 100% while the others are at the nominal 10-20% so over all, for a 4 core CPU for example, you'd only see 30-40% CPU utilization. Feel free to verify this by observing the per-core performance of your CPU.

And that is, of course, assuming that your bottleneck is not your flash player or browser, which might have a lower resource cap than your hardware.