SVD XT - image2vid - image detail deterioration as videos get longer

I am testing SVD in comfyUI using the image2video conditioning. When I render 25 frames at 1024x576 using the SVD XT model, I get reasonable detailed images. But if I render exactly the same schematic but for 100 frames, the image detail deteriorates dramatically, much resolution.
As a further test, if I render at 2048x1080 for 10 frames, I get a close copy of the source image. But, if I render the same schematic with 25 frames, the detail also deteriorates.
Is anyone else suffering from this?
Is there a way keeping the same detail across the 100 frames?
Many thanks

Render 10fps 2048x1080

25 frame render of above