I documented this arc flare years ago in my review of the Zeiss ZF.2/ZE 21mm f/2.8 Distagon but I decided to update the flare page documenting the behavior across the aperture range. Large examples are shown from f/2.8 - f/16.
The ZF.2 and ZE version behave identically.
According to Zeiss, the lens coating on the new Zeiss Milvus 21mm f/2.8 (same optical formula) should greatly mitigate or eliminate this type of flare, which would mean an outstanding performance, since other types of flare are exceptionally well controlled in the 21/2.8. I am hoping to obtain the Milvus 21/2.8 soon to confirm the behavioral improvement.