[Brightcolours]

I was there, no other people were taking pictures, no flashes used, the issue happened in another picture but it is less severe, pictures taken à fraction of a second before  or after affected pictures have no issues.

So, like Markus explained, the IS of this lens (EF 35mm f2 IS USM) apparently jolts during the taking of the image after it thinks the image has been taken.The exposure time according to the camera is 1/80th of a second, which the lens thinks is the duration it needs to freeze the image. But with silent shutter, the duration of the exposure of the whole image is longer going all the way from side to side (in this vertical case), probably something like 1/30th of a second.

I suspect that if you would use the RF 35mm f1.8 IS STM Macro instead, with silent shutter, you would not see the same issue, because the IS will behave differently (take 1/30th sec into account).