Random FPS drop after the client has been opened for a while

It is still a thing. The solution is to completely remove all remnants of Synapse 2 and use 3. Known Technical Support Issues - #16 by Drakuloth

If manually removing the last of the Synapse 2 files mentioned in that post doesn’t remedy it, you may want to look for temperature spikes with HWMonitor. These can throttle the hardware off/on to control overheating.