When 2 PEPd threads (typically on different hosts) will try to create a
particular mapping at the same time, they may step on each other and both back
out of the operation; in such cases it appears that the file representing the
proxy may be left behind, which then prevents further attempts to map that
proxy: if the file is present, it must have a link count of 2, else the code
fails.
From Maarten description on GGUS:
Related GGUS ticket: https://ggus.eu/index.php?mode=ticket_info&ticket_id=117125