After updating my project from 4.18 to 4.19, I started getting huge FPS drops at regular intervals. I managed to trace back the issue to particle systems with mesh emitters and could reproduce the problem in an empty new project with a default particle mesh emitter (download link below). The FPS drops start out small, but get progressively worse the longer the editor is open.
The issue appears to only occur on Nvidia GPUs (tested on GTX 970, GTX 1080, Radeon R9 200 Series).
Result: The editor will stutter in a set interval. The stuttering gets worse the longer the editor is open. The more particle systems with mesh data are in the level, the shorter the interval between the FPS drops.
This is a regression. This issue does not occur in 4.18.3.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-58676 in the post.