Actor's axis flickering in viewport

Hello,

I am a beginner on unreal engine (version 4.20.3) and a strange thing happens when I select an object in the viewport. its axes (green, blue, red arrows) are flickering.

After some research I noticed that if I disable the option “realtime” in “viewport options”, the problem disappears. But I would like to understand why this phenomenon appears ?

I noticed on more thing : When I change the quality of anti-aliasing (in setting-> Engine Scalability Settings) from epic to medium, flicker disappears and I can let the realtime enabled.