Mythic Silken Court has had massive desync issues since the launch of Patch 11.0.5. Here's how you can still defeat the boss.
First, let's explain how the telegraph and damage actually functions. The damage event for Spike Eruption is when the spikes appear out of the ground. The telegraph of the brown rings exploding is NOT when the damage event occurs. The telegraph only shows you where the spikes will fire. Before the patch, the spikes would fire out of the ground a consistent short duration after the ring explodes.
However, with the launch of Patch 11.0.5, the amount of time between the ring exploding and the spikes actually firing has been made inconsistent and variable. You can see how late the spikes can actually fire compared to the ring in these clips below:
Knowing this, it means that you can outplay the bug. The fight is harder and the telegraphs are misleading, but it is possible to defeat this boss.
The goal is straightforward: once a ring explodes, you have to wait until the spikes actually fire before moving through it. Just because a ring spawned first doesn't actually mean that the telegraph is going to explode first.
Hopefully this bug will be fixed soon.