Concentric rings on aurora photos

[glaopt1]

Hi

I took photos of the aurora - exposure about 20-30 secs - with a sony A7M3 and 28-105G. In the centre of each photo concentric grey rings are visible. Any idea what causes this?

Prior and subsequent daytime and lowlight photos do not show the grey circles. I attach a sample here you can see the rings just below the main cloud.