Confirmed still happening in 5.1.
The suggested fix of System->bCompileForEdit = false does not work in 5.1 (Lyra project). It still always spends 30 seconds doing this same dumb repetitive nonsense every time I start the editor.
LogNiagara: Compiling System NiagaraSystem /Game/Effects/Particles/Environmental/NS_CharacterDash.NS_CharacterDash took 29.178122 sec, no shader worker used.
LogNiagara: Compiling System NiagaraSystem /Game/Effects/Particles/Impacts/NS_DeathCubes.NS_DeathCubes took 29.041485 sec, no shader worker used.
LogNiagara: Compiling System NiagaraSystem /Game/Effects/Particles/Environmental/NS_ElectricMovement.NS_ElectricMovement took 28.778368 sec, no shader worker used.