I had forgotten to turn off debug logging on department's printer server during the previous year.  Today the printer server had run out of disk space, since it was full of debug logs. This has now been fixed.

If there are any Linux hosts, which do not see any printers at all, it probably means that the local printer spooler daemon (cupsd) has died because of an unrelated bug, triggered by unresponsive printer server. This can be fixed by restarting the Linux hosts or asking system administrators to restart the daemon manually.