I have saved twice, looking closely for different plants (to distinc the screenshot of save on menu) ... for the second time it saved and it's ok for now.
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Same for me, on XBOX One version. I'm at the Inactive Lava Zone, 600m from the Castle, it was the last valid save for me.
My game loading is now about 215 seconds ... I can load, I can play but it wont save again.