This looks like https://forum.step.esa.int/t/snaphu-import-problem/4264/29 from 2017, but should have been fixed in the current snaphu version. What is in <snap_install_dir>/.snap/auxdata/tool-adapters/Snaphu-unwrapping/version.txt? Mine has 8.0.0. Have you tried running snaphu from the SNAP 8 GUI?