Hi,
we have the same issue since a few days. Nothing changed on our side.
I don't know if this link is still up to date but this troubleshooting guide doesn't help : Troubleshooting: Previews
We also have the {%22_tracker%22:%22z9Ng7jyV%22}
value for io.prismic.preview Cookie. Deleting it doesn't change a thing.
Can anyone from Prismic team can help us ?