The path to feedback HTML files contains a timestamp and, thus, a colon. If the jupyter-fs lab extension is installed next to nbgrader, colons are not allowed in paths (the colon is used internally by jupyter-fs to prepend a 'drive' to paths). Navigating to the feedback files in JupyterLab users get an error message, that the path does not exist.
This issue could be solved on jupyter-fs side, but since colons in path should be avoided for other reasons, too (see this discussion on stackexchange for instance), nbgrader maybe should avoid colons in paths.
The path to feedback HTML files contains a timestamp and, thus, a colon. If the jupyter-fs lab extension is installed next to nbgrader, colons are not allowed in paths (the colon is used internally by jupyter-fs to prepend a 'drive' to paths). Navigating to the feedback files in JupyterLab users get an error message, that the path does not exist.
This issue could be solved on jupyter-fs side, but since colons in path should be avoided for other reasons, too (see this discussion on stackexchange for instance), nbgrader maybe should avoid colons in paths.