Disabling vsync/uncapping fpses might help.
I experienced strange issue with 5.4 and older versions where vsync/fps lock causes editor to halve its fpses the more windows in ue editor there are open.
If you manage to find way to replicate the lag, you could try recording with unreal insights (performance profiler) or software like very sleepy the exact moment the freeze occurs and check the function stack while spike occurs
Might help. Theres also possiblity that high temps of cpu/gpu cause throttling to lower temps as failsafe which might be causing stutter/jitter