This is part bug, part feature request.
Bugs:
Never create a permalink that is longer than the maximum URL size.
Features:
If the permalink has to be cut to not extends the maximum length, then, when clicking on the permalink, we should advise the user that some of the facets will not be saved in the permalink.
Give a feedback in the UI that not all facet will be saved. Maybe following the permalink, add « (some facet are not saved) ».
Put in the documentation that the facets are saved from the start, and that if there is too much facets, that at one point, facets data will not be saved.
Regards, Antoine