FWIW, I've built proxmox-backup-restore-image packages (for PVE 8.1+) that use the 'ntfs3' driver instead of 'ntfs', if you want you can give them a spin and see if they work better for your snapshot:
http://download.proxmox.com/temp/file-restore-ntfs-3/
Code:$ sha256sum *.deb 23aeab40e58a130901d2b023e11339903dd90dd8ef11cb5caae8d7bafa32596c proxmox-backup-restore-image_0.6.1~test1_amd64.deb 0f6e4746cc9408bdc3c3d81c0834531eb8fdaaa94ffd2a804a02b7c6581e6a52 proxmox-backup-restore-image-debug_0.6.1~test1_amd64.deb