Strange Lensflare-Flickering - Renderbug

Hi there,
I was wondering when I packed the Photo-Studio-Template of 4.24.3, that there were flickering frames caused by the lens flare effect. Did anybody of you had this issue, too? Most of the time the rendering is brilliant, but sometimes you see frames like these (see image or video…_0403.mp4?dl=0 )
It is only visible when packed or in the standalone player. I found out that the problem is the spotlight in the back. If I delete it, the flickering is gone. But why?