I also noted the snapshot problem after I upgraded my witness nodes to HF25 last week.
Starting my witness nodes from a snapshot I got a weird "popping blocks" error which was fixed by stopping and restarting the witness node.
I referred to this in this post: https://peakd.com/hf25/@apshamilton/witness-node-upgrade-to-hf25-hiab-hf25-snapshot-available-for-download